Ranking sucks. This is the biggest reason anyone would spam. If there were no ranks it would be better. Because this site wouldn't need to ban or warn anyone for this. I do think they are cool and all but, it starts a lot of stuff. Also I think they should keep the "Junier Memeber, Heroic etc" stuff.
There will be warnings and bans regardless of how the ranking system works. People spam because they like to see their post count rise. Also because they think it's funny. So altering it wouldn't prevent people from posting useless garbage. There are still other reasons.