A joke that would be funny in 2 minutes gets dragged out for 5+ minutes.

That's because they have to fit in commercials. If they have a 2 minute sketch, they would need to have another 3-5 minute sketch as filler before the next commercial. Instead they drag out the 2 minute sketch for 5 minutes, when the joke of the sketch really only deserved 2 minutes.

That's one thing shows like Monty Python's Flying Circus did well. Because there were no commercials on British TV at the time, they could make each sketch last the right amount of time. If something was funny for 1 minute, they could do it for 1 minute then move on. If something was funny for 12 minutes, they could do it for 12 minutes rather than cutting it to fit in 7 minutes.