'Ass' in American English is a fascinating bit of language. I'm not sure that this isnt more of a Linguistics question, but I'll have a stab at answering.

A lot of authors have focused on the use of the -ass suffix I AAVE (African American Vernacular English). See https://languagelog.ldc.upenn.edu/nll/?p=36421and https://languagelog.ldc.upenn.edu/nll/?p=15735for some links to relevant research. However it appears that this use may well have originated in WW2 military slang, and became associated with Black English subsequently.

John McWhorter discusses its use in AAVE Iin a couple of book at least- Talking Back, Talking Black and Words on the Move, among others. This a link to an interview (text) where he talks about it in some detail.

However, the grammaticalisation of -ass (the process by which it took on the role of intensifying suffix) probably began in part vía the existing polysemy of the noun 'ass', especially in its use to refer to 'one’s self or person, either referring to the specific body part, or metonymically representing the whole person' the self, and in part as an extension of the use of the phrase 'big-assed', initially literally meaning 'having a big ass', moving on to describing planes with large rear sections, before being applied to anything unexpectedly large. Then, presumably by a process of assimilation and ellision (where sounds are affected by the sounds around them, or are dropped) and reanalysis (when we recategorise a word we have heard 'incorrectly)', or by the laziness/innovation principles as per Guy Deutscher in The Unfolding of Language, big assed became big-ass. Then, by a continued process of reanalysis/grammaticalisation it went from bigass, to badass, lame-ass, and all the other -asses we hear today.

Beyond my hazy memories of my own reading I got a lot of this from this masters' thesis, which is available online: Grammaticalizaton in English: A Diachronic and Synchronic Analysis of the "ass" Intensifier by Wilson Miller of San Francisco State University.