It's impossible for me to sit on a trainer and stare at a wall or TV. I'd gain weight over the winter and come spring it would take several months to get back into good riding shape.
Zwift is a blast and makes the time fly. I find I am pushing myself harder racing on Zwift than I do out on the actual road.
I've also got a couple friends in different states. We join the races together and talk jive while we go.