A relatively low percentage of users * the total number of people who buy smartphones = a heck of a lot of users. If they manage to pull those people away from other companies (and such a future would do that), it's a big win.
Take webOS which you could put into dev mode (essentially rooting) by entering the Konami code (upupdowndownleftrightleftrightbastart ).
Didn't seem to do them a bit of good. So easy rooting may be a desirable feature but doesn't seem to sufficient feature to ignore other more important features.