It may just be that you're on a low population server. It's probably too early, but I imagine SE is looking at world populations and is likely planning on a merge at some point.

As for cross server party finder, I'm not a programmer/cs whiz so what follows is pure speculation based on my primitive understanding of the internet but:
Duty Finder works cross server because instances are not server specific
However, character data (names, jobs, etc.) is server specific. A cross-server PT finder would require a server to look at ALL the other servers at once. It would be a great feature and would be amazing to have people from all different servers in a party, but um memory limitations perhaps? I unno. again, not a programmer. For all I know, this is entirely possible and SE should look into it.