Because what the world wants to see is 12 exhausted players limping around the field after playing for 150 minutes.
I agree, its one of the things that completely turns me off about basketball, for example, is the constant checking of time at the end of games. (not to mention the 100 time outs each team gets) "lets add back 2 100ths of a second on that last play!" I like how the CR is in charge of time and no one but the CR knows exactly when the match will end. I just want the CR to recognize and punish excessive time wasting by adding that time back at the end as a way to combat such excessive time wasting
The hypothesis (which may or may note be true) is that the combination of play till a goal and fewer players creating more open space on the field will mean that the extra time would be very unlikely to last the 30 minutes we currently play. I'd like to see an experiment to see if the hypothesis is true. If we saw games going 150 minutes, I'd agree the model sucks. (I don't see that happening.) Indeed, if we saw games going past 120 minutes on anything other than an extremely rare basis, I'd call the model a failure. My guess is most would end by 110 minutes. A goal from open play would be a much less unsatisfactory way to end a game than a missed PK. YMMV.