Even if they were always going to speed things up, you'd think they would have planned for multiple seasons, with the first one indeed set hundreds or thousands of years earlier - though of course that means only their Elven characters could carry over into later seasons. Which is probably why they didn't do that...

I guess there aren't too many major obstacles to lumping everything together like that, though. They'll just have the Rings working quite rapidly, while Elendil and Isildur are establishing Arnor and Gondor.