"why are their two standards? why not just go to one for everyone?"
For the same reason some countries measure in miles and some in kilometers.
NTSC (National Television Standards Commitee) came first, then somebody decided that could do better and came out with PAL (Phase Alternate Lines). The differences are that PAL handles analog differential phase better than NTSC does.
Contrary to popular belief, the 60 fps 50 fps frame rate difference has nothing to do with it being PAL or NTSC but is due to the fact that Europe (which is on 50 Hz power) adopted PAL (as well as SECAM in some countries) while the US stuck with NTSC and the US is on 60Hz power.