I think guys are pretty much just indifferent to makeup with or without unless it’s the first thing they notice about the girl’s face (In that case, it would be wayyy too much).
To us, because we are so familiar with our faces, makeup causes us to undergo a huge transformation.
For example, I have a very slightly asymmetrical jaw, and I never noticed it until I was 13 and got braces and my orthodontist brought it up. Now, ever since I was “enlightened” to this imperfection, I notice it in EVERY single picture I see of myself. I’ve told other people about it, and they swear that they can’t see anything. But it still bothers me.
Same thing with makeup. We keep covering up the same flaws that no one besides ourselves really notices, and are afraid to leave the house without mascara because we feel it makes us look “so much better.” Seriously, I have known girls who refused to go running in the dead of night in their neighborhood without eyeliner! Another friend of mine bought like more than $50 worth of special waterproof makeup to wear to the beach because she hates how she looks without it. Guys (with a few exceptions) don’t wear makeup or feel the need to wear it because they have grown accustomed to the way they look without it. Makeup really can be an addiction! The more you wear it, the more you are dependent on it. The truth is, aside from concealing pimples etc. and maybe adding a little dazzle, makeup doesn’t make a girl look BETTER, just DIFFERENT.
I don’t wear makeup all the time. When I do, it’s just enough to make me look like I do at my best without it. I’ll hide that occasional pimple, add a little color to my cheeks, and wear clear lip balm. If that’s not enough, then I’ll add a tiny bit of feathery mascara (not black for me; brown) That way I avoid the whole “omgsh she looks like a different person without her makeup!” dilemma.
I think this is honestly what most guys prefer, and I can’t think of a better way to explain the “why” of it. I hope this was helpful!