Kasparov had an amazing tournament record but he played surprisingly low number of tournaments. Carlsen plays much much more number of tournaments compared to Gary and still got an amazing score.
I think you are confusing Kasparov with someone else. He played all the top tournaments, and won almost all of them.
Maybe you counted all the meaningless online tournaments for Carlsen? I don't know.
Kasparov had an amazing tournament record but he played surprisingly low number of tournaments. Carlsen plays much much more number of tournaments compared to Gary and still got an amazing score. When you play less it's easier to maintain quality since you have time for preparation, but when someone is playing continuously and yet winning all without fail, I feel that's more impressive. Also Carlsen sometimes plays weird opening moves against his opponents like h5, a6 etc and yet manages to win. Gary on the other hand relied deeply on opening preparation. Magnus plays pure chess and doesn't rely on preparations to outclass his opponents. Also in World Championships Magnus lost lesser number of games. So for me Magnus. Sorry for the long answer. It's my first.