I don't think they're being negative, just practical.
The bottom of the seat flips back so if you're just covering the back of the seat, then it won't be seen. If you sit on it, then it won't be seen.
I guess the only thing is to put the bin liner on the seat after the game when the bottom has flipped back up. But if everyone has left, then it won't be seen.
Sorry if that sounds negative too.