Gameplay is a buzzword. Any "true gamer" always values gameplay over graphics. Or rather: "True gamers" insist that modern and/or popular games games focus on graphics over gameplay. God forbid a popular game having really good graphics!
But what does good gameplay mean? Does it mean playability? If so, then the opposite of good gameplay is unplayability. What does an unplayable game mean? Does it mean something like "I really like the idea behind this game and it has nice presentation, but it just feels like I'm fighting against the interface trying to do things?" (Maybe more specifically "Wow, those aliens are cool and these guns are cool and boy does this game have good graphics, but man are these controls laggy", or "Why won't you jump into the direction i'm pointing the stick at? NO, DON'T JUMP INTO THE CHASM!")
Is there any game that has bad gameplay but still has millions of people just shrug and go "well, the graphics are so nice that I'll just keep on playing?" My guess is no.
Ah, so, a partial point emerges: If bad gameplay causes a game to sell poorly, why would a company release a game with bad gameplay? I think this is pretty well known and thus no "real" company releases games with bad gameplay.
Personally I can think of only one game that has had bad gameplay that I have liked. That game was Chicago 90 on the Amiga. It didn't even have that nice graphics. The mouse pointer moved really jerkily (yes, on an Amiga) around the screen, and the main gameplay window had a pretty poor framerate and if you crashed your car (as the bad guy) the game was over. Regardless, I just thought the game was fun. It was fun to try to outrun the cops, and as a police, it was fun to try to corner the bad guy. But that is just my personal opinion as I don't think the game was very popular.
And that is my main point. A game has to be fun. Bad gameplay often lessens the fun quite a bit, so it's not completely irrelevant, but if the game still manages to be fun, you can take you gameplay and shove it.