What’s the incentive for a developer to inflate their estimate? The only reason I have to inflate an estimate is if I know some non-engineer boss-type is going to swoop in and try to convince me to lower it.
Deliver under estimate and get a bonus, raise, influence, or just plain old "well done"
Be lazy and only work half the time while delivering "on time".
Only work on the project half the time, spending the other half on something more worthy/interesting.
This is actually a pretty common motivation for devs who work under legacy management.
Under-promise. Over-deliver. I'm not doing software development most of the time but it absolutely works out better for everyone concerned if I get things done on or ahead of schedule without mostly having to resort to a lot of unnatural acts to do so. If there's a real need for something faster, I'll tell people I'll do my best and (usually) I can get there absent blockers from dependencies. But I try to manage things so that I can meet/beat estimates sanely. It probably helps that people think I work quickly even given some sandbagging.