It was actually most likely due to contracts. The actors were all due to renegotiate their contracts and be due a pay rise. That's part of the reason Starfleet academy was greenlit because the cast would be cheaper and reuse the 32nd century assets.
I think it's really bizarre to be against representation in a tv franchise built on representing the other, whether they be Russian, Japanese, black or LGBT. Like what the actual fuck do you think star trek is about?
I am absolutely not against representation.
I just think it's a disservice to those being represented if that's blatantly the only reason why they're there.