But that does not work on lobsters (or anywhere else with gated registration), because you cannot just create 10 accounts. You can create 1 account after 1 invite. If you abuse, you loose the invite (and maybe the person inviting you the right to invite others).
I think, if i have understood the answers correctly that it's stopping a quick proliferation - but not a long slow infiltration?
The spam bots I regularly deal with on reddit are using accounts that are several years old. I'm not sure if they are hacked, purchased, or something else.