Mirages are separately instanced sub-areas, so why disable portals?

This is just an unnecessary annoyance. You can only take back one inventory of stuff... Woe will be you if you happened to go in with a bunch of stuff.

So you...
1- warp to Mirage entrance
2- exit to map
3- TP to hideout, vend
4- re-enter map
5- re-enter Mirage, run back to the loot
6- warp to Mirage entrance
7- exit to map

The amount of travel and zone transitions is absurdly inflated.