How do you know that?
This is just something I commonly see throughout life. I know you've heard someone say "it ain't mine" or "I didn't pay for it".
Think about it...if I give lesson for free and they don't practice, what have they lost?...nothing. But if they had to pay for lessons, then they stand to lose something if they don't practice.
I paid for my lessons. It cost me a couple of lessons when my instructor wouldn't go any further until I learn my previous lesson.
E.g., I have a daughter who tore up the car we gave her; would never check the oil, even after I showed her how. But when she bought her own car, she's faithful to take care of it because (I believe) she paid for it. A lot of parents deal with this issue with a lot of stuff they buy for their kids.
Another example, people will tend to treat a rental with less care than their own car (especially if they have insurance).
Have you ever lent something of yours to someone who broke it, and they returned it nonchalantly like it's no big deal?