As for why nobody tags their posts, I have no idea but outright laziness is my working theory thus far.
As for finding gay-themed images, hi, I'm Lothar and I'm here to help.
The tags "male_only" and to a lesser extent "male_focus" are your best bets overall.
Don't bother searching the "male" tag because a shocking percentage of the results will be paizuri pics in which the only part of the male you can see is either his crotch or his glans.
This may be obvious, but if you find a pic you like, check out the artist's other stuff- Just because one of an artist's pics was properly tagged doesn't mean they all are, and you can help correct that.
Slightly less obvious but often a productive tactic is checking out the other posts from whoever uploaded the pic you like.
Male-specific tags such as "beard", "hairy_chest", "smooth_skinned_male", and "nude_male" can yield good results too, but penis-specific tags will often get you a lot of futanari pics in the mix.
Or, if you like your guys beefy, butch, and hairy (along with some I just thought were cute or funny) then check out my Favorites and work from there.
Good luck finding pics you like, and welcome to Rule34.XXX.