Because of the way different sounds developed in English and in languages that English got words from, the sequence "ooch" tends not to regularly arise in words with the most common kinds of origins.
However, that doesn't prevent "ooch" from occurring in words that are onomatopoeic (in a broad sense) or sound symbolic. I think sound symbolic words tend to be perceived as more colloquial than words with other origins, so if "ooch" words have a higher percentage of onomatopeia than other words, that might explain why they are more colloquial on average.
Why "ooch" rarely developed in the most common sources of English vocabulary
In native English words, the “(t)ch” sound arose from palatalization of an earlier /k/ sound. A palatalizing environment would usually also include or affect the previous vowel; for example, the vowel in beech is the result of palatalization (also called I-mutation or umlaut) of the same Proto-Germanic vowel that developed to oo in other contexts.
In words of French origin, an o sound before ch usually developed to “oa” (as in coach, approach, broach) while an /u/ sound (spelled “ou”) usually developed to the diphthong /aʊ/ (still spelled “ou”) as in pouch, couch, vouch (or occasionally instead to u as in scutch from Old French escouche). “Brooch” is a spelling variant of “broach” that was originally pronounced the same way.
In words of Latin or Greek origin, ch pronounced /tʃ/ does not regularly occur (there are a few words like conch where it has come to be used as a spelling pronunciation).
Some of your specific examples
- brooch: as mentioned in the previous section and in user6726's answer, this word has an exceptionally archaic spelling and would regularly be spelled the same as "broach"
- cooch: unclear
- gooch: unclear, I think (I can't find an etymology given for it)
- hooch: according to the Oxford English Dictionary, from "hoochinoo", from Tlingit Hutsnuwu
- mooch: possibly from a somewhat irregular or dialectal alteration of French Anglo-Norman "muscher" according to the OED
- pooch: unclear
- scooch: unclear, possibly influenced by scoot
- scrooch: possibly one variant of a number of related onomatopoeic forms
- smooch: fairly unclear, possibly onomatopoeic or a dialectal variant of an onomatopoeic word