I have two machines one an i5 4690 another an i7 6700 and have two vives, one(I7) has single player horde mode the other(I5) does not! I had to stop and think

I have two machines one an i5 4690 another an i7 6700 and have two vives, one(I7) has single player horde mode the other(I5) does not! I had to stop and think about the word "vives", heh. Of course I was not expecting someone to describe his partners' gaming setup, but still tripped me up. This seems like a weird thing to do, and perhaps even more so that it wasn't more clearly communicated. I don't follow this game at all, but there are clearly commenters who do who are surprised about being locked out.