"Why not serve fake garbage indistinguishable from real content by a computer, like LLM output?"

Serving more than the minimum wastes resources. Worse yet, a better solution would cost my time.

"Sending errors just incentivizes bot owners to fix the identifiable parts"

Sure, someone could make or configure their scraper perfectly. "Perfect" is now the table stakes though.

Edit:

My solution strives to cause an unproportional expense in order to circumvent. I want 10x on my time.