LLM’s use dashes a lot because there’s a limited sense in which they’re extremely good writers- LLM writing is easy to read, and LLM flow is good. Dashes are great for flow and comprehension because dashes are best interpreted prosodically - as a call for a certain sort of pause- rather than grammatically.

Modern writers are taught to think of punctuation as a grammatical instrument, but it’s much easier to follow writing in which punctuation is treated as a prosodic instrument. The dash is the refuge of prosody. Incidentally, this is how I generally use punctuation. It means “pause here for a bit”- not some godawful nonsense about clauses.