I would not say that the main issue is the complete lack of enthusiasm, what I see are two things.

In some instances these people are rather interested in doing something more than they did as a dev or they are interested in leadership itself, but not in the subject matter itself, so these people want to assume more responsibility or they are interested in leadership itself but not in the subject matter they supposed to lead.

The other thing I see is in the western promotion culture, there is a pressure both on the employer and on the employee to promote and be promoted.

"He's been working here for so long, he needs to accept more roles and responsibilities or something is wrong with him."

"I'm at the company for 9 years, as a senior dev and architect, I just feel that I don't want to get stuck in project work forever."

So I kinda feel that people are not always interested in the subject, the either just want to move on or they are expected to move on.