So why there still bitcoin developers in the play?
Maybe they have a hard time leaving ?
Well one thing is developing, and another thing is promoting and selling or changing for the sake of change.
I agree that there is likely very little need for development with bitcoin, except to entertain the possibility of possible changes, tweaks with the passage of time... so for example, scaling will likely always be a bit of an issue... to not make too big and not allow to stay too small.
Also, if an improvement proposal is made, there is likely needs within a community to assess whether such a proposal is capable of achieving consensus, and certainly developers could be sufficiently familiar and articulate enough to assess possible technical issues.. so in the end, it seems quit logical that with an adequately programed coin, such as bitcoin, changes to the protocol would be extraordinary occurrences rather than something that took place on the regular.