IIRC they updated parts when SB hit. They're actively trying to get out of the crap infrastructure that they were left with on 1.0 that they couldn't toss going from 1.2x to 2.0 because it would have taken more time.
That said, I'm also wondering if it's because of the multiple OS it has to run on? While yes, at the 2016 FanFest they said "please upgrade from Win32bit to Win64bit" not everyone can afford to. I'm not a programmer though so that's a wild guess. Anyone who is a programmer around to confirm/deny that? The most I know is that they're different in how things are run, but any programming for a Win32 or Win64 is beyond me.
Lastly, I remember when we had a delay on some of the smaller in-between patches after Heavensward came out because the dev team was taking a much needed vacation after pounding out not only 2.0 and its releases, but up to 3.0 with no breaks in-between. The amount of salt and people on the OF screaming about HOW DARE THEY BE LATE FOR THESE YOU WANT TO WATCH YOUR GAME CRASH AND BURN SHUN THE NON-BELIEVERS leads me to believe that while some are totally down for no content for a bit while they fix infrastructure, there will be more people screaming about how there's no content how dare they want to fix their game they're using it as an excuse to take a long vacation etc etc.
Yeah, I'd love for them to do it all in one go, but I don't see that happening. They'll update the way they did with SB and probably some unnamed patches. My guess is that's where the saddlebags are coming from is a small update on a part of the old infrastructure.