Why are some songs popular and others aren't? It's an intriguing question that I don't have enough info to answer. I'd probably need some psychology and background info to get into it.
Well, I can't really tell you the "why" in terms of psychology, but I do know some common denominators of the "how".
The major thing that I think of is the so-called Four Chords of Pop, or I-V-vi-IV progression. You can hear these chords really prominently in the hook of Don't Stop Believing by Journey, but they're in a metric
ton of pop music. This chord is part of why so much of it sounds really samey. I don't entirely understand how it works because I don't really understand music or musical theory (I won't even notice the chords unless they're pointed out). There's variations on the particular formula, but it's nearly omnipresent, and it's at least one factor in making music catchy and highly consumable in mass markets.
Another might be the constant use of love and romance themes, or feelings in general, really. Music is really not a medium meant to spread complex thought, although, my boy Melodysheep does love to try.
As for my own opinions on mainstream music, well, I like it, generally. That enjoyment could very easily be chalked up to, again, my lack of knowledge of music, or simply lack of taste. I love everything from the sugariest and lowbrowest of mainstream pop music (Owl City, Katy Perry, early Lady Gaga, 3OH!3) to classic rock to complete hipster bait. I've seldom met a song I don't like.
I can tell you one mainstream song I despised though: Katy Perry's "Roar". God, that song was awful, absolutely no energy to it, no flavor, nothing to be gained. And I've loved lots of Katy Perry's hits. Come to think of it, most of what she put out post-Last Friday Night kinda went downhill.
I could talk about this stuff all day, really. I listen to way too much of it. I could have a 3 hour conversation with you about the intricacies of 3OH!3's Streets of Gold album and how it's actually a stealthy warning about how having everything you could ever want handed to you for no good reason will destroy your mind and your soul, and lead to a path of self-destruction. Seriously, I actually recommend Streets of Gold if you can stomach 44 minutes of the "crunkcore" style and the lack of real talent. It's an interesting album.
Goddamn, I talk too much.