Well, I.S. development got into stale after AkaTsubaki broke the balance. Other Fourth Generation unit don't appear until five years after the story, for example.
Space Exploration more or less available again, and I.S. being less useful for military show of than they're carrying helium from Lunar mining operation (where else you get Deuterium aside form Jupiter?)
At least until Alien began to appear since Earth was recognized recently, had reached scale I Kadaschev for the first time. And then realized that they have the equivalent of I.S., lot's of it.
The bridge gap seems to be useful though, now for the next generation... maybe a perfect human-I.S. hybrid?