I disagree that it would be (technologically) hard for Bitcoin to transition to a PoS (disregarding that we don't have yet conclusive proof if any PoS model actually works long time).

Ethereum is built to a spec. That's why the different client developers had to coordinate their work. This is not the case with Bitcoin. There, the official client is the de-facto spec you have to comply with if you develop another client.

The bigger problem is that the current narrative of Bitcoin heavily discourage hard forks.

Transitioning to PoS would be a social task with Bitcoin, not a technical one. Also note that Ethereum was promised from the beginning to transition to PoS, they just didn't expect to take this long.