There are some that aren't chance! For example, an emordnilap is a word that gains a new meaning when it's written backward; the term was coined by flipping the existing word "palindrome" (a word that has the same meaning when written backward). Or in electrical engineering, the unit of conductance is the mho (the unit of resistance being the "ohm"). The technical term for these is ananyms.
However, most of these examples are fairly straightforward. Anyone who sees the word "emordnilap" with its will know it's not an inherited English word, and probably look for deeper meaning.
All of the ananyms I know of come from languages that already have a writing system. Written language requires breaking words up into units which you can then rearrange freely, but this isn't at all an obvious step for people who don't write. For example, ananyms in Japanese and Korean tend to reverse the syllables instead of the phonemes, while the English example emordnilap would be pronounced something like /ə.ˈmord.nɪ.læp/ rather than /mwoɹd.nɪl.ˈæp/.
Another way to think of this is: what does it mean to reverse a word? Until we had record players we couldn't actually reverse the waveform; a human vocal tract certainly can't. Reversing the phones? That requires a clear way to draw a line between phones, which even with modern spectrograms we can't do. Reversing the phonemes? If you asked a person on the street to reverse the sounds in the word "pineapple", they most likely wouldn't be able to do it: at best they'd write down the word backward and repronounce it according to English spelling rules. Even in your examples, you're relying on the spelling rather than the pronunciation.
TL;DR: Flipping words around simply doesn't seem to be part of human language; we simply don't have a mechanism for it (unlike, say, reduplication, which people can do trivially). As such, we don't see any examples of ananyms until the origin of writing—and even then, they tend not to really catch on.
