If you’re an employee who can finish their work 25% faster but you’re not getting a 4-day work week, what are the incentives for not introducing creep?
Just sitting around and thinking of solutions to your own problems beats giving yourself work. As refactor_nietzsche would put it, resource slack is what lets you be a refactor_master instead of a refactor_slave. If you feel pressured into self-imposed creep, it's probably because you've internalized the idea that having too much slack makes you look dangerous to your superiors, so you default to playing the worker bee.
As someone who really hopes developers get much more productive in our team, I would hope we are able to finally keep pace with the desired roadmap and fix bugs at a much faster rate so customers don’t have to wait too long for things to get fixed. Currently, we always get late and the roadmap has to be changed to remove less important things so we focus on fewer things. Which is not ideal, we are definitely losing business when we drop items, and we know that since potential customers keep running into use cases we knew would be useful but never managed to get to.