The sages instituted the Bracha MeEin Sheva on Friday night because shuls were located in the field and if someone would be late to minyan, he'd be endangered by having to walk home alone.
On a weeknight, no one went to Shul due to being late at work and would rather Daven at home (!), so the Rabbis didn't see a need to institute this blessing.
But Yom Tov doesn't have this blessing either, which implies that no one went to Shul on Yom Tov night. Why not? It's not that people can work into the night?