That's like asking why senior/staff engineers tend to review more code than write themselves. In certain environments there's a scaling constraint, and you can generally have wider impact through oversite than typing at a keyboard yourself. That's not to say one is more worthy of your time or not, just that it's not unique to AI.

Generally though, you are also investing your time into leveling up junior engineers to take over responsibilities from you. I just never really see that happening with AI. Even as it gets "better" technically, there's no real growth pattern to its work and it doesn't understand ownership or responsibility.

But if scaling isn't a problem, then sure just write it yourself.