The different lines on a court are boundaries for certain things, like serving. When calling a match, for fair play, the ball has to at least touch the line when it’s compressed by maximum downward force. So a ball that looks like it didn’t touch the line may very well have but a ball at a lower velocity may not. That’s why there are two officials with good views of the boundaries.

So not only are we talking a lot of cameras, most would need to do super-slo-mo and be cost prohibitive. They would also have to account for velocity and why on earth am I writing about tennis scoring at 1am omg I have to go to sleep.

Hope this helps!

E: this is confusing because I’m tired. I can explain it better tomorrow 🤪