Most other groups want US to reach the world for Christ. We are all in it together. All participating. All members of Christ's body moving through history for Christ.
Actually, a LOT of groups in the U.S., mainline denominations in particular, tend to think about "us and ours" and not work well with others. Many groups have their own presses and only use their own materials (Baptists in particular, others as well). Or their own seminaries. If you're a pastor in a mainline denomination it's not so easy to switch to another and still be a pastor. (It can be done, but not easily!)
I still remember when I left GC and joined a Baptist church and a friend asked me "How long have you been a Baptist?" Well, I've been a
Christian since 1987...
And I believe this thinking is hurting the traditional mainline denominations whose attendance is dropping... many people aren't into doctrinal differences and have no "brand loyalty" anymore. So what if I leave this group and join that group? And if you're claiming you've got the one true way to go about it, that's a turn off to me...
But yeah, GCx has always had an attitude of we've got it right, much righter than those other people out there...