For LFS to have an AI pace car, the AI would have to be, well, decent. Right now they're a work in progress and the devs know only too well that the AI need improvement. That's also why the AI didn't slow down - their "I" is very "A" right now
Also, a yellow flag doesn't automatically mean a pace car - most of the time it means "no overtaking in this sector - be careful" unless, of course, it's a
full course yellow - which often does mean a pace car's coming soon. I'm just going by F1 and V8s, dunno what you're used to watching ...