I have the same problem too, I feel like maybe you drop out because you already got what you got from them or maybe you don't really feel like working on the project, you just think that you should.

I still feel pretty bad about this and have a lot of guilt by not pursuing my projects, however I recently finished reading "Refuse To Choose" by Barbara Sher and it was a game changer, I still feel bad about it but I see now a different perspective and it has given me hope and made me realize that perhaps I'm not as broken as I thought I was.

The book also has a bunch of tools to help you pursue your goals even if you tend to rotate interests, that's another thing to like about it: not only is relatable but it's also very actionable.