#1 answer for me. Cheap balls can play inconsistently due to inconsistent weights and sizes, even extremely small differences are noticeable with experienced players. Not so noticeable with occassional weekend players or people that haven't put in thousands of hours playing with a good set of balls.
lol
Years ago a friend of mine got his first table. He went out and bought a cheap set of brand new balls from Kmart for around $35 while I put Simonis cloth on his table. The table played slow compared to every table I'd played on with Simonis, including mine. He wondered if we should've replaced the cushions. I told him it wasn't just the speed off the cushions, but something overall was just off. CB reaction was different, the balls didn't break well, etc... I went home and got my set of Brunswick Centennials and we rolled those puppies out and that table came to life, played great, excellent speed, excellent cb reaction, etc... He took the cheap balls back to Kmart and I ordered him a set of Centennials.