You don't understand how games work.
Achievements track 'a thing', and when 'a thing' is done you get a sticker.
It gets steadily more and more complex the more stuff is actually in the game. Tying that in with online servers makes life even harder.
For this achievement, you can't track 'capture a point', because there are PvE points and they'd count too.
You can't track 'capture a point in WvW' because then the achievement would be completable after the event ends.
You can't track 'stand in range of a WvW point when it completes being captured between the dates of x and y', because that's a ton of wasted data being sent, or calculations on the server for the rest of the games life whenever a point is captured.
There are a TON of things that can go wrong. Especially seeing as how we aren't even playing WvW anymore, we are playing a separate branch of WvW v2.