I agree, when there is a huge glut of good (hyped or name brand) games being released, the lesser known games will likely get passed over. Often, the lesser known games are actually better than the "big" games. Yet, people don't buy them because there are other, better known games being released at the same time...which get all of the attention and, thus, people's money. The other games don't really have a chance. If the game releases are more spread out, there are less new "major" releases to detract from the purchase of the new, lesser known games. If people don't buy the lesser known games, sequels will likely not be made...no matter how good that game was.
I see the psychology as similar to the movie industry. The most money is to be had when the movie/game is first released. A lot of people buy on impulse because it's simply a new release. If you put off buying a game because there are other games that you also want (which are also being released at the same time), you may actually end up not buying that other game...a newer game may be released, later on, which you then want more...and there's that psychological tendency to always want to buy the newest game/see the newest movie. So, you may end up missing great games while buying rubbish games because they were simply hyped new releases.
Sure, if you have loads of cash, you can buy every game that you want. But how many of us have THAT much money? Spreading games out also allows us to more easily pick and choose which games to buy. We can more easily pick out good games from bad games and more wisely spend our money on what we really want.
Does that make sense? I don't know if I explained my stance on this clearly enough....