I don’t really care about the things I don’t care about. I’m too busy with the things so do care about to notice the things I’ve lost interest in. I’m not sure what the “last” thing was.

sure, I would say many things gradually lose their importance, but what's most important to you reveals itself to you over time, and those things still matter

I lost interest in 7 Days to Die (the Steam game) but my interest always circles back around every now and then

Life inflicts on us a lot of social warfare and when you avoid contact to people who do so you take that warfare less seriously and also those people. I observe I reduce my contacts since the importance of having many "friends" is greatly outweighed by the stress they do cause. I lose interest in people who clutter my mind with the toxic things they bring to me.

Well, that statement is a reduction, and it sits solely on the negative side of life (or maybe it's saying things not mattering is a good thing, I don't know). Life is many things, though yeah, it's true that it's a dark world. But, as some things get worse as we age (such as our declining looks and health), other things get better. 1. we get wiser, and 2. I think what happens is we become more and more "ourselves."

Yes. Life.

Life can also be a progression of things gradually gaining importance until we die unwillingly.

I lost interest in GTA V because I can't buy it in order to play online.