I'm surprised at this for a number of reasons.
Any single competent network engineer would just drop AS13414 at the border, and be done with it (And AS35995/AS54888, since Twitter have multiple AS's). However that's not the case... So I can only assume the technical advisor to the government either didnt want to have a functional ban in place, or was not competent enough to advise correctly.
I'm also surprised that Twitter dont start the whack-a-mole game of spinning up EC2 instances as light weight reverse proxies for their service, then GeoDNS to target Turkish users.