Why ? Because I don't see any useful purpose to the rolls unless I can do them properly on real surfaces.
A guy I met, with ~6 years of Judo experience jumped off a moving car at 30mph (he had to, at that point - its a long story) and rolled... on the road... he had a few scratches but that is all.
Thankfully it was late and there were no other cars nearby.
So like I said - I see no point to rolling if it's only learned for the purpose of "playing on the mat" without any regard for unpleasant, unfortunate real-life circumstances.
I remember running in the park about 2 years ago... I was an idiot, plus haven't taken Aikido yet, so I decided to run as fast as I could, coincidentally I tripped at really high speed, landed on asphalt and got some skin off due to sliding.
It stung like hell, plus my elbow was hurt, and something else... I dont remember it very clearly.
However, I know that if the same thing happened now,I wouldn't be nearly as injured because I wouldnt hesitate to roll.