Because it's the only efficient way to level.
On my first class I was a FATE beast, when I realize how much exp it was giving me and how fast I got to 37 I stopped doing them a lot ( I still do them only when they are near me).

I been doing the other content so I just don;t sit there FATE grinding my life away, course it's not the most proficient way to level but I am having FUN! I don't understand why people that "Hate" FATE grinding torture themselves just so they can get there first 50 or any 50 for that matter.

I'm leveling at a steady pace and having fun, I still don;t have my first 50 ( but that's because I'm doing other things to level, NOT just FATEs)

I am in no way telling anyone to do what I do, FATE to your heart contents, just while your doing your FATEs and before you complain, please know that there is other way to level up ( whether they be fast or slow they are there).

In accordance to you, doing no FATEs and playing 1 class to 50 ( 46 being what you have now) over 1 month into the game is not rushing. Your just about ready for 2.1 when more end-game content gets pushed through the pipes.

There isn't. I've done it all, and doing it for another job would be nothing but endless repetition
That's how you personally feel about it, in that case I can only suggest you to wait 1 or 2 patches for content to funnel through so you can play your 1 and only job.