Why cant i fly 6-7 weeks after major knee surgery?

I am 13, almost 14, and nearly a month ago i had major knee surgery. They broke part of my shin and rotated it, they put in cadaver ligaments, and scoped out some damage. I found out a couple days ago that my doctor doesn't want me to fly due to blood clot risks but isn't my surgery far enough out that i would be okay? I was going to go to florida but my doc said no to heat and amusement parks, so we thought while my family went there i could go see my grandparents somewhere else and just chill. Do you guys have an idea of why he is saying no? I REALLY wNt to go!