In Test cricket the team aspect of cricket comes in due to the extreme length of the game. Sri Lanka could just bowl all day with Murali and Vaas, but that's physically impossible and they'd break down, forcing the other bowlers in the team to step in. Similarly batting for long periods of time is extremely draining, and if as side wants to bat 100 overs they will inevitably need to rely on other batsmen to contribute.
In One Day cricket, you could very feasibly have Vaas and Murali bowl the majority of the 50 overs, with maybe some fill in from Jayasuriya and the likes to give them a breather. You don't need the other bowlers in team to contribute. You don't even need other bowlers. You will still need batsmen, as the need to score runs quickly causes wickets to fall, so while its quite easy for 2 batsmen to bat out 50 overs physically, it is extremely difficult for them to do so while also attempting to set a competitive score.
Limiting the number of overs per bowler put the emphasis the team aspect of cricket.
Occasionally your two best bowlers will knock over a side quickly and you won't need other bowlers, and your two best batsmen will click and you won't need the other batsmen. But those instances are rare and are a result of exceptional skill. For the large part, OD cricket has been pretty well designed to allow the best team to win, and not the best players. Much like Test cricket.