I think there is a steeper learning curve with developing for Bitcoin than with Ethereum programming (not that Ethereum programming is easy). EVM chains have a lot of boilerplate code written for you from various ERC standards. People are likely coming from that and expecting / wanting to write high level apps on Bitcoin but finding it less trivial than forking some contracts.

EDIT: Also because Bitcoin is seen as the hard money in crypto, I think there's probably a mental barrier of taking precious BTC savings and using them to tinker within the ecosystem.