The claim that right-to-left emerged because of chisel technology was quoted from Quora by the Children's Museum of Indianapolis website as a potential theory, and was also on Wikipedia's article on Right-to-left script. User ShreevatsaR wrote an answer on English StackExchange in 2010 to the question Why is English written and read left to right?, with the caveat that it may be an urban legend. It is noted that generally, hieroglyphs did have to be painted or drawn on the stone surface first before carving; red ochre and black chalk seem to have been popular choices.
Medium cites the top-to-bottom then right-to-left method (as employed by the Sinosphere but also commonly on Egyptian papyrus) as being functional for those with right-handed dominance, because it allowed the left hand to unfurl the scroll as the right hand was writing - another Wikipedia citation, this time on the page Horizontal and vertical writing in East Asian scripts (still extant as of early October 2023).
Both of these claims were nonetheless espoused in a published paper - from the International Journal of Pure and Applied Mathematics by Y Nishiyama (2010). The first claim is also the titular one from the 2008 book Why Hebrew Goes from Right to Left: 201 Things You Never Knew About Judaism.
Some data on hieratic on papyrus comes from a chapter by Colette Sirat entitled The Material Conditions of the Lateralization of the Ductus, in the 1988 book The Alphabet and the Brain: The Lateralization of Writing. The example in the image there is the 18th Dynasty hieratic papyrus E 3230 A from the Louvre.
The scribe held the unused portion of the roll in the left hand, while writing with the right. The written portion fell by the right side of the body, and as writing progressed, the papyrus could be rolled up again if it began to unravel. This control using the right hand was very simple when sitting on the floor.
However, 'tablet and stylus' for Sumerian cuneiform differs in quite a large way from 'papyrus roll, ink and reed' for hieratic:
The form of the signs, as well as the materials used, show that they were written with a raised hand, and, as we would predict, the horizontal lines ran from left to right. The tablets were palm sized, and were probably held in the left hand.
A 2019 Linguistics SE answer from Ilmari Karonen gives further insight into the mechanics of cuneiform and some more inscriptional evidence.
It is perhaps useful to use WC Watt's classification of written systems into eographic, neographic, mesographic and cenographic. Only at the mesographic stage, where rapid writing of large quantities of text, does a 'standard' cursive system emerge, making 'ease' the main factor, dependent of course on the 'hardware' available.
The Greek alphabet is standardised in the sixth to fifth centuries BCE, before which there was much more variety in direction. But this had been preceded by a large increase in literacy through the eighth century BCE, moving all of these into a 'mature' mesographic phase:
This movement of true alphabetization was seen amongst the Phoenicians, the Canaanites, the Israelites, and the Greeks. Reading and writing ceased to be the privilege of scribes and became accessible to all people, whatever their rank might be.
So the real question here is why the split of the Greek tradition from the Semitic tradition of writing. Sirat ascribes this to the socioeconomic perceptions of writing:
The almost absolute dichotomy that we see in Greece between writing as a profession and writing as a means of communication is based on two principal reasons. The first is intellectual, affirming the superiority of speech over writing. Writing was never the "sacred character" or the "divine writing," but an inadequate transcription of discourse. [...] The other reason is related to uses and customs, which prohibited a free Greek from sitting on the ground. In fact the Greeks, like the Assyrians before them, never sat on the ground but always on seats.
A different (and admittedly even more obscure) explanation for right-to-left (or the split of the left-to-right from the right-to-left among mesographic written systems) comes from D. de Kerckhove, in the chapter Logical Principles Underlying the Layout of Greek Orthography, where he says that abjad systems are contextual for readers i.e. "reading will depend primarily on pattern recognition", rather than being a contiguous system as the modern alphabets are. From this, it is concluded that:
Consequently, the types of scripts that require speed of feature recognition to establish appropriate contextual relationships (such as consonantal alphabets) will be read to the left of the visual field better than to the right; while those that require speed of connecting the contiguous relationships of the sequence of characters [...] will be read better to the right than to the left of the visual field.
The author then cites the Etruscan alphabet and the Kharosthi abugida as right-to-left counterexamples. Further on, the same author cites some neurobiology, while classifying abjad 'words' as being iconic in their neural processing:
In addition, it appears that within the visual system of a normally lateralized - i.e., right-handed - subject, the right hemisphere is better at deciphering icons and images, while the left is better at analyzing sequences. [...] These preliminary observations first led me to speculate that, all considerations of posture and writing material aside, iconic and pictographic writings might favor a kind of neurological processing quite different from that which is elicited by phonological systems.
Personally, I think this is a fascinating, if murky, topic, where epigraphy meets historical art depictions and neurolinguistics during a period of social upheaval and the consolidation of traditions. It is bound to have been a multifactorial shift that 'standardised' the directions of the Semitic scripts - after all, according to Astoreca (2021):
[I]f we look at other writing traditions, not related to alphabetic Greek, it is not uncommon to find long periods in which writing is not visible in the archaeological record, after which it is usual to see a continuity in the writing system that shows that writing was not abandoned altogether but has simply disappeared from the surviving record and cannot be traced. This is the case of the Cypro-Minoan syllabic scripts of the 2nd millennium [...] Similarly, Semitic writing also experienced a gap between
proto-Canaanite to Hebrew and from Nabatean to Arabic.