I think that companies view 'the anime market' as something with in-built preconceptions and expectations of content and they market towards that, hence we get straightforward Gundam shows over here like the dire G Fighter, yet genuine oddities like Turn A or Victory stay shelved. On the other hand, maybe it's just that they're series with 40+ episodes compared to one-offs, OVAs, and movies, and as such would cost more to repackage and/or rescore for the west. There's always the internets, mind - if nothing else, you avoid having to listen to painful English dubs.
I'm pretty sure we've got a good lump of the Gundam stuff over here, just a few of the series are missing, like Victory, X, Turn A and ZZ, but they're all available online - just remember that using the internet to watch tv shows that aren't available to buy as dvds is killing the industry of selling dvds of tv shows.