rust is a small map meant for small games. if you are going into demolitions, domination, tdm or any other 12+ person game you wont see it. its not in the playlist rotation for them, thats why you wont see them.
You can skip RUST, it's just like the map Shipment in CoD4 in size. If you haven't played Shipment I can say it's a really small square map. The only gametype fun enough to play on Rust is FFA. Kind of hard to play any other gametype in that map.