Because then people would start complaining because they've changed something. Just like people didn't like Enterprise because the characters were more human (like we are today). Many Trek fans don't like change.
Yeah, people would complain, they always do. Can't ever meet the expectations of rabid fanbois.
And, FYI, ENT failed because it changed to little, it was essentially TNG/VOY light up until season three when it was more a re-hash of DS9/BSG.
and as for many Trek fans not liking change: Who cares, as long as it sells well to the average moviegoer.