I've noticed this watching pros at Indian Wells. IW hard courts are very rough. Some players would wipe down their outsoles between games during practice because they had picked up a lot of tennis ball lint.
Yup most indoors here have either an electric or push sweeper machine for the lint. One club I used to play at was so lazy about cleaning up I would slip all the time, almost put out my knee. Didn't renew the following year!
I run my hand over my soles once in a while during play and most of the lint comes off. Picked this up playing basketball as a kid. If you watch a basketball game closely you will see players doing this. They’re not dealing with lint but a little sweat on the sole makes shoes grippier and removes the sweat from your hands.
Just penn HD balls I've used a million times.
These courts just got resurfaced a year ago and haven't been used much, plus I invested in a new rotation of shoes (close-out asics court speed ff) recently. Guess the combo of new surface+new shoes is velcro for ball lint.