A friend and me played singles the other day,we usually play doubles but two guys could come this time so we decided to do singles,and a couple of days later confessed that he has not been so tired from a workout for very long.
The fun thing is that he is doing badmington and spinning a couple of times per week.
I however tried to do some running this summer,i could run like 500 meters then had to walk for a bit and so on,but i can play 2 hours of singles,sure i get tired if i meet someone that can make me run alot,but i make it...
The point is that your body can be different,my friend can do spinning for 1 hour nonstop with a trainer pushing the tempo,i would probably last tops 5 minutes if i held back hehe
I really have bad cardio but somehow tennis works better,maybe your body is more responding to normal cardio but is less adapted for short explosive starts and stops.