The reasons are not obvious to me. Why did they stop? Cheating? Annoying support requests? Could sell for more money?
My idea is the free version has some drawbacks:
(1) people don't want to pay will stick with this free version
(2) it's like a sample pack for solver, you may download the free version and say "it's not so good after all". Bad for business
(3) it increase the probability of been hacked