Chainsaw Mage said:
Neither response really answers the question, which is why the games take so long. I'm not complaining, or anything;

I'm just puzzled.
In test match cricket: Each team has two innings, each of which lasts until either all ten wickets have been captured, or until the batting team 'declares'. The game has a five-day time limit, which (broadly speaking) is not extended depending on the weather. To win, you have to score more runs than the opposing team after all four innings have been concluded. If the fifth day ends before the final innings is complete, the game is a draw.
Because the innings last an undefined length of time, the game itself will inevitably last a long time.
In one-day cricket: Each team has a single innings, capped at 50 overs (300 balls bowled). To win, you must score more runs than the opposing team.
In twenty20 cricket: As one-day cricket, except an innings is capped at 20 overs (120 balls bowled).
American football and baseball are highly tactical sports, with much shorter games. If a cricket game were "capped" at, say, four hours (and yes, I've heard of the new 20Twenty format--or however one phrases it

) what would happen?
One day cricket is entirely different in complexion from test match cricket. In TM cricket, it is quite common for one team to find themselves with no real chance of winning, and the game becomes a battle between the batsmen and the bowlers, with the batsmen not trying to score runs to win the game, but rather battling to stay 'in', to run down the clock.
Additionally, a cricket team will typically be made up of players with different skills: you have your top batsmen and your top bowlers. In test match cricket, everyone has to bat, and that requires a bit of caution from the top batsmen - they can't go wild in case they get put out cheaply, and the team suffers. But, with one-day cricket, it is likely that only a few people will have to bat, which means the top batsmen can be a bit more adventurous. If they lose their wicket cheaply it doesn't really matter - the next guy is probably a top batsman too.
All of the considerations with one-day cricket also apply to twenty20 cricket, but to an even greater extent.
There's probably more to it than that, but I'm not an expert on the subject. Both my father and grandfather have followed cricket for years, though, and are rather dismissive of the one-day and twenty20 forms - they like the longer strategic battles of the test match version of the game. To them, the length is a feature, not a bug.