Why don't you have handles on the back of your chair?
Everything in the disabled world is about safety. Ridiculously slow lifts, sheltered workshops, disability tax to every level of unwanted consultancies.. this is no different.
It's to keep you safe.
Touching my chair is like grabbing my ass without my permission. It's not welcome and when people do that, no matter how well intentioned, I react poorly. And by poorly I mean with violence so since it's not likely someone attempting to assault me will warn me, I've made sure to maintain public safety by eliminating the temptation. ☺