This mod for one totally changed my game and I am sad to see it stop, and I did contribute btw. To my mind it adds in the missing components KSP needs, a sense that we are not stuck with an advancing Space Program without refinements in the basic capsules, etc.
You might want to consider getting on Patreon, which allows for a recurrent monthly donation to be set up, I believe Bob Palmer (aka RoverDude) has had some success with it, but even with all he does I don't think he makes all that much. We live in an age of (perceived) entitlement, free music, free video, free porn, etc available through the Internet and people forget that it takes a lot of effort and time to produce. Because you can easily get it doesn't mean it was easy to produce, a lesson that is lost with digital replication unfortunately. I can't say I blame you for giving up, but I do believe modding is an act of self-gratification bolstered by the knowledge there are many folks you will never see or know who employ your work.
I would implore you though to consider allowing someone else to develop while you are off on other things, you never know you might want to pick it back up one day. If you simply stop development and walk away forever quite frankly all your prior work is for nothing really as no one will continue to use the mod, which would be a real shame in the long run, better to let someone else pick it up for a time. Mods really should be treated as an Open Source development effort, wherein others can pick up where you left off as you pioneer other mods.