It's possible they had the bare bones of a time travel story, and just lacked a good reason for them to go back to 1986. Or at least a reason not done before on the series.

There also might have been budgetary reasons to do a movie mostly set in the present.

I wonder if a Gary Seven cameo was ever thought about?

It's been so long, that I don't know if talk of Kirk and company becoming an intergalactic version of The A Team, was a real thing, or just a joke that was going around. Ditto the Eddie Murphy rumor.