Well, the reason is cost. Gmail works well because when you click on it you get a few milliseconds of resources on thousand of computers. The rest of the time

Well, the reason is cost. Gmail works well because when you click on it you get a few milliseconds of resources on thousand of computers. The rest of the time those computers are doing something else. The economics aren't great for any organization that doesn't have those boxes laying around already. Also obviously Google has search technology laying around in their kitchen drawer. If you don't have that you are starting at a disadvantage.