It's called being the straight/white/cis male main character of the team. It always annoyed me that Cyke had love interest after love interest following the Dark Phoenix Saga, while Storm was single forever until Forge came along. Kitty got a love interest right away!
All two of them? Post Dark Phoenix it was just Lee Forrester and Madelyn Pryor. Colleen Wing was previous, and in total Scott has had 6 love interests in his publication history (although he did have 4 in a relatively short period). I'm not counting alternate universe versions nor ship teases that didn't go anywhere, but I am counting Frenzy even though that required reality manipulation powers rewriting history and ereasing other characters from history in order to make it happen.
It always amazes me how Scott's relatively low number is too many when other characters need a scientific calculator and a spreadsheet to keep track of them all, and I never hear complaints about them.
Dark does not mean deep.
Do other characters need calculators? Who?
The only romances we hear about are the true love ones or the ones where someone is being manipulated. In reality, there would be a lot more casual hookups. Personally, I think comics are very conservative when it comes to this.
Lots of comic readers will deem anyone with more than two relationships to be a ho.
I think it has more to do with most books just don't take the time to give the characters personal lives. The recent X-Men Monday interview with the Simonson's reminded me of this, as Louise pointed out that she made an effort to show that connection to the life outside of being in X-Factor for all of the characters, so they all had relationships to various degrees of success (poor Candy Southern).
I am not sure comics are too conservative to portray more casual hookups, it just becomes a mess. Either fans like the hookup and they are stuck with it, or at some point every characters has hooked up with every other character and it just makes it hard to believe that all these people being in the same room with their exes is not just super awkward.