Why? To discourage you from giving free copies to 20 of your friends.
10 is a generous number already, and if you need more because you like to format windows 5 times a year and use it on your desktop and laptop, then contact support, explain why, and they'll give you more.
There are lots of IK policies I find strange or just don't agree with, but the 10 activations thing is not one of them.