I wonder if it is demoralising. Imagine any project you worked on for multiple years - and someone suggests it could be rewritten (and better) in a long weekend. How would you feel and respond? I might laugh a bit, but I probably wouldn't spend much time on it.

The part of FOSS I think would be demoralising for me would be dealing with all the people who assume that the maintainer of a piece of software is a customer service operative who exists solely to reply to them in a timely fashion.