I would say the main reason for Pakistan's defeat is bad captaincy. After 7/8 overs when India were under a lot of pressure after losing several wickets, the Pakistan captain used his spin bowlers. The spin bowlers did not give many runs, but they allowed the Indian batsmen to settle down at the crease. And I think this is the main reason for Pakistan's defeat. Pakistan will have to play more carefully in the upcoming matches if they want to win and want to qualify for the next round.