Pac isn't just Dragon Gate's champion, he's also got an unbeaten streak going on there. They've lost several of their top guys recently, so they're building up Pac as this unstoppable monster so that hopefully whomever beats him eventually we be established as a new top guy. And other promotions (RPW, OTT, etc) have been willing to play ball in this regard by having Pac's matches end in DQ's, time limit draws, etc. But AEW doesn't want to do stuff like that right now, and Dragon Gate doesn't want him losing in another promotion while they're doing this story with him. So it's a case of two ideas clashing.
Also Japanese promotions tend to be very protective of their top champions in general. They don't lose in other promotions as champions except for VERY rare/specific and pre-agreed upon situations. For example, Okada might wrestle in ROH, but he ain't losing there while he's champion, NJPW wouldn't allow it.
I think that it'd be different if Pac weren't the champion.
Also BeastieRunner, I doubt that Jericho is beating Okada. NJPW and AEW don't have a working relationship right now and while I'll never say never, they've surprised me in the past, I don't see what they gain by putting the title on Jericho when he's not even full-time with them?