1. Github or other public Git repositories: Wouldn't be complete
Haven't published everything always, don't want to publish everything, would want to include everything but couldn't. So using public Git repositories would always be accompanied by a feeling of imperfection.
2. I've never used Git for anything really.
Apart from cloning and occasionally updating others' repositories I've never used them. I'm not used to using Git and I don't struggle with not using it. So starting to do so now would require me to hurdle quite some hurdle. I never used it. Why would I start now?
3. It's too late to start now.
I've noticed that the point where it would have been a good idea and would have made a lot of sense to get accustomed to using Git has long passed. So by starting now or in the future I would admit that I didn't take the hurdle when it would have been the right thing to do - when the best time to do so was near the present. I would admit to doing some things not the right way in the past if I would start to do them right from now on. It's easier to pretend that the way it always has been is the right way - the way I'm used to doing things.
That all makes no logical sense. It would be an improvement to start using Git for some things, be it coding projects, any category of texts that I have on my computers, any collection of files, ... The costs of these improvements would be hard disk space, which isn't all that rare for me nowadays and getting used to using Git, which isn't complicated.
So why don't I even try to use it in some cases? Well, I've just honestly told you my three reasons.