Interesting 🙂 I wouldn't naturally assume this would work, because we don't often see conveyor belts in the real world made out of cloth, presumably for the reason you mentioned, that cloth doesn't easily hold enough tension to be useful in a conveyor situation !
However, if you change a couple of things about the animation and your mesh, we can probably make it work better than it is now !
1. Your belt needs to be even polys in the direction of spin, so not quite the variable density you have going on now...
2. Move the rollers away from each other during the start of the animation so tension is increased.
CBR