Not necessarily (just) ego. It's also that greenfield is much, much easier than brownfield. You can make your own decisions, rather than first having to learn what others decided for you. You can start with a naive blue sky vision of the product, not yet tainted by all the complexities that will only surface when you really get into the weeds of the problem you're trying to solve.

> After all, that's a problem already solved: CLAs for open source.

With CLA's in place contributors usually sign away their copyright, often to get rug-pulled when an open source project reaches a certain maturity and popularity, and the commercial plans are activated by the company behind it. Better look for community-driven projects that come with a DCO [0] instead.

[0] https://en.wikipedia.org/wiki/Developer_Certificate_of_Origi...

> Take for example, the bajillion expenses tracker apps. The most reinvented wheel. Do we need yet another one?

Well, small projects being repeated is one thing, but because they're small there's only so much waste there.

I'm thinking more about "cathedral-like" projects, some massive open source project that lasts for years, in which it may be important to emphasize the contributions of, and a particular way of understanding the contributions of the many stonemasons and lesser artisans, as opposed to the leadership of the project and the architects.

Our whole society would benefit I think by having more respect for the "average person that contributes to the common good, even if they're not the leader", and actually praising that as much or more in some cases than the leadership role.