Of ledges and you
Those ledges likely are there instead of some invisible walls (which GW2 does have a lot of anyway), so there’s the possibility that you might end up in a place where you’re not suppose to be.
A video game is never going to allow for every single movement option that exists in real life; you have to draw the line somewhere. While a full parkour running/climbing system might be cool, I doubt whether it’s the best thing the developers could possibly spend their time making.
Not to mention that all the existing maps were presumably designed with the current movement limitations in mind; anything that lets players cross an obstacle that they previously couldn’t would theoretically require an audit of every existing map in the entire game to make sure it doesn’t break anything. Just like they couldn’t realistically add jumping retroactively to Guild Wars 1, any fundamentally new movement options will probably have to wait until Guild Wars 3.