It's a mix of reasons. Many of the core devs have been jealous of ethereum as long as it's been around, and want to bolt EVM capabilities onto Bitcoin. Some bitcoiners don't have faith in Bitcoin as peer-to-peer electronic cash and think it needs these capabilities to succeed. Many are simply reacting out of cult-like zealotry. Any implementation other than the Core GitHub repo is blasphemy and the core devs are the infallible high priests of Bitcoin and should not be questioned. No matter what is wrong we must all stick together for the sake of consensus and the prospect of a chain split is unthinkable. Finally there are many who are unknowledgeable and unthinking and simply follow whatever their favorite podcaster or influencer edge lord says.