It's an entirely different codebase. Lemmy is written in Rust, PieFed in Python. If you're a Python developer you're not going to randomly learn Rust to contribute to the huge existing codebase that is Lemmy, and even if you did you might have a different stance than the Lemmy developers calling for a fork.
Furthermore, it's not a zero sum game. The projects share content, and both benefit from the success of the other.
Open source is all about fragmentation. It's a natural result of freedom.
Sure, if everybody pulled the same direction on the same project and successfully coordinated their cooperative effort while agreeing on everything and also having the perfect™ vision for the project, that would be great.
But that's just not gonna happen, for a million reasons. So instead, we get diversity, and people can use the software that fits them, and develop what they're interested in in the language of their choosing. Thank god.
Open source software is everywhere. Even freaking chromium is open source. Android is open source. WebKit is open source. Pretty much the entire web runs on Linux servers. Even gamers buy devices running Linux now.
Is it not mainstream because people don't realize it's open source while using it? Isn't it rather that it is mainstream when people use it without even realizing?
Normally I'd agree, but the recent increase in popularity of Pixelfed among the TikTok crowd has shown me that it's possible for one fediverse platform to succeed where a competing one failed.
I'm fine with it whilst there are maintainers with the whole "transgenderism is bourgeoise decadence" stance going on. I've happily worked with MLs and MLMs, I'm not a fan of bigots who work backwards to fit their ideology to their prejudices.