I've said it over and over - the changes in the timeline WENT BOTH WAYS. Future *and* past. (Instead of a "Y" shaped branching, imagine an "X" shaped one.)
It has to go both ways, if you just stop and think about it - otherwise nuKirk and co. could travel back in time to any number of events, and hook up with the Prime Kirk and co. or the Prime Picard and company, and then travel back with them into a future that isn't their's!
Star Trek's future has always interacted with, and influenced, it's past - via time travel - so we even have a *mechanism* for how the changes in the timeline could propagate both ways: change Trek's future, change it's past too!
Hence, the Alternate timeline has a different tech level.
(It's even possible that imho, "before" Picard and co. went back to Bozeman Montana in the 2060's, that, like someone else said here, Archer was a Daedalus captain, in one version of events. (The effects of time travel in Trek have never been consistant - though the Star Trek Department of Temporal Investigations books try to address how the different types of time travel changes can exist in one...er...reality...ish..whatever...(multi-reality? over-reality?)