Because the Vasari (lore-wise) have the most advanced Phase Space-related technology. And because Phase Stabilizers are what make the Vasari powerful.

If you give them to the other races then that's as good as defeating a Vasari opponent at the beginning if you play a large map.

This is what makes the factions DIFFERENT. In Sins WE DON'T WANT THREE FACTIONS THAT LOOK DIFFERENT BUT ARE EXACTLY THE SAME!! We don't. It's just WRONG.

Thus, I advise you to give up on this mod. It can only bring problems to gameplay, with the TEC+Advent becoming far more powerful against Vasari than they already are, especially if these gates are lower-tier techs than the Vasari one.

And asking people to make models for you isn't really useful. The modelers who frequent the Sins forums/game are often busy with other projects.