That's because segwit was badly implemented. There's no buttom on QT to create segwit addresses, you have to use a console command.

You cant expect the average user to be writing console commands, specially when most of them dont even have patience to synch the entire blockchain, and prefer smartphone wallets instead.

Also, segwit only gave me a 15% discount when I tested it. To send 100k satoshis, you still need to pay approximately 80k satoshis in fees, sending from a segwit address.