This person sounds similar to me, in a way.

If he is like me than just taking this track through life's course is the one most comfortable. Maybe he doesn't get enough happiness out of challenges, unusual things, new experiences, to make all this worth the effort and energy and disruption that it causes.
Thoughts don't pop into your mind as often, and when they do, they seem filtered and when they aren't, it all seems too much to bother with.
Call it lazy, call it selfish, call it narcissistic. That's just interpretation.

Then, unless he becomes conscious of it and calls it a bad trait he has to work on, he won't come up with ideas for activities, or plans, or take initiative.

I don't understand why someone is saying you mention no good reasons for being with him. You say you have nice conversations, that he cuddles, that you have similar values, similar personalities, makes you feel comfortable, hardworking nature, strong empathy. And there's probably more as this is a topic on what you have problems with.

Sounds like consciously, he tries to adjust his behavior for you, but in the end deep inside he is the same person and he can't consciously change his subconscious. We don't get to pick our personalities and even the idea we get to pick our decisions is tentative.

What can be done? Is there really no improvement in his behavior and stagnation in the relationship?

I suspect that you dumping him will come as a surprise to him, will hurt him more than you suspect, and may worsen his 'problem'.
But maybe I am projecting too much of myself on him. Not that his life is any of your responsibility.

Maybe he takes you for granted and is truly a narcissistic.