As your parent comment says. It’s about trust. People don’t hire contractors with low reputations. Same with SaaS services. That’s why you see so much stuff about branding and customer testimonials. It can be gamed, but usually works well enough.

LLM have no reputation to lose. Their work may or may not be aligned with your goals and they can’t care if they messed up.

Personally, if my company would have one person write a utility which mine would depend on, and that person would quit soon after delivery, I would be pissed. And I would demand that my team take ownership of the utility, and gain intimate knowledge of the utility, and voice my concerns with management who made the decision to hand out a task like that to a single person. I would then inform that management about the concept of bus factor, and how they just violated best practices. That next time they decide to hand out a task like that to a single person, that they should instead just hand it out to the team which is gonna rely on that utility.