Tldr : "even though the things are shit, it's my shit so I'm not going to clean it" attitude.

The tread in question started with improving interoperability between software and remove branding them from the so there won't be mastodon this, pleroma that.
Instead there would be standardized fields and images support and the branding would go in the hands of community (aka whoever is running the instance).
The reason to increase the adoption.

The point is the tread devolved into shitfest because many of them simply don't care about branding or adoption, because things are working for them like how they want.