Because my phone wont let me uninstall it [0] and it's not just on my specific phone, other manufacturers do the same. I also cannot uninstall Amazon or the 5 other completely useless apps it brings, Facebook Messenger and Instagram are ingrained into my phone which is annoying. I wish rooting and setting up a custom ROM wasn't a painful experience or I would do both, but I like getting updates, which rooting stops, and I'm not too sure a ROM supports updating properly.
[0]: https://www.reddit.com/r/androidapps/comments/3catb0/i_cant_...