I know what you are saying, I think there are multiple causes for this.
The key issue is due to the over abundance of porn, before internet was readily available, porn was much more difficult to obtain, especially gay porn, you either have to go into shops and buy them in front of others/facing the shop assistant, or have to order by mail which is a problem if you live with family or friends. At that time just nudity would be a major turn on and would be really hot. By now you can get full HD porn at your fingertips any time of the day, just vanilla porn becomes the "norm" where we feel indifferent about them, they are just the same thing with slightly different looking people in them. I think that might also be the reason that porn actors get more prominent tattoo these days - it might help them stand out from the rest of the industry, at least for me, that's what Logan McCree stood out when he first appeared in porn.
I wouldn't say that the studios dictated how men should look, the "Mainstream" (and I use that term loosely) porn still favours the type of twinks or guys with athletic or muscular bodies, so they are still the type of guys that major studios pick up. I find that along with fetish videos, if a particular theme/type is different, people will be more likely to be drawn to them, ie outdoor sex, particular gear/uniform, but as soon as this happens, it will either be extensively featured by multiple studios or a particular new studio would become a key/main provider for them and pumps out a large number of movies that they become the "norm" again. Quick examples include spanking videos by Sting/Helix, Public videos by Outinpublic, "Amateur" videos by CzechHunter, Sketchysex, Cross Generation videos by iconmale etc etc, even if you look at Czech gay fantasy videos, that was something completely new and I found it to be really hot at the start, but as the third or fourth volume came out, I couldn't be bothered downloading it anymore. It is more like that we become accustomed too quickly with any type of new or exciting porn, and they just don't do it for us anymore.
I certainly agree with what you are saying but unfortunately I can't think of anything that could change that, maybe is the new challenge of porn in this era? LOL