Reason:
It is just way to cumbersome if you are frequently changing skills to always have to go through the list and find (and remember at times) the skills you want for a particular build. Then you have to get them in the right places. It's just one of those things to make the game play more smooth.
Additional ideas:
It would be cool if you could name them too. For example you could have things like your "healer" or "Destroyer" or "Experimental" skill sets. And even more ambitious task would be to include attribute points distribution and armor into the build. If this were to happen it would be a one-click to a completely different build for your character. Anyway I'd be happy just with the skills.
