By limiting the number of people that can play with one copy of a game, more copies of the game have to be bought to have the same number of people playing.
I know that some people might not buy a game because it doesn't have splitscreen but there might also be people who buy an extra copy because they want to play with a friend or something but can't do the splitscreen.
People who want another SW Battlefront: 201 "Gnarly, you are clearly more educated than me" - OblivionScamp
Like sarisuppius said, it's not about sales. We're now in the 3rd generation where so much emphasis has gone on graphics that gameplay often suffers and for good or ill we're not at the stage where you're pushing the hardware that hard that it's just not capable of split screen and quite honestly it's such a minority market these days that it's seldom worth the effort to cultivate that market by creating a gimped game mode.
Yes my username is Subtle Joke account, if the best retort you can come up with is "that wasn't subtle" you already lost.
The hardware limitations excuse is pretty lame IMO. They've been doing split screen since the days of SNES (not sure if the NES had any spit screen games). Even on an older 3d system like the N64 or PS1 they did it and they made it work. It usually took a hit in texture quality and a hit in fps, but guess what? If somebody wants to play split screen they're going to play it whether or not it gets 30fps or 15...
IMO it's mostly just laziness, not sales.
"You shouldn't be asking HOW things are, given that we already know there is something..but rather WHY things are, as opposed to there being nothing."