They became big enough because they were free and had massive cash behind them to destroy all competition (Mapquest, Garmin and others)
Now they are this big, they have become quasi public record for many other organizations who rely on this data.
Since they want to keep costs low, if their data is wrong, it can have significant impacts on your life and getting someone to correct it is almost impossible.
Want to, not really. Want GMaps moved from Google? Yes. If it can stand on it's own free, fine whatever. If not and people need to be charged for it, fine.