It's true that it's easy to do, but I think the better question to consider is: what would a person actually accomplish by doing that? By intentionally staying tiny (assuming they have the resources to do otherwise), they're limiting their targets to other nations in that range. The vast majority of those in range will be newer nations. so most of the time they would just be knocking around new players without the means to defend themselves.
If they're roguing due to boredom with peace, it's a pretty cruel way to go about it, and it probably wouldn't even be particularly entertaining given that their opponents wouldn't be capable for fighting back in any meaningful way.
If they're roguing for casualties, they'll barely get any at that size.
If they're roguing due to a grudge, their grudge is probably not with those newer players.
If they're roguing to try to be a nuisance, the damage they do at that size can be fixed with an aid package or two (unless the event is discouraging enough to the new player to drive them from the game entirely, but that would be a loss for the whole community given the state of the playerbase).
As far as I can tell, pretty much all online games of a sufficient size have a contingent of griefers, so they must get something out of it. Probably not anything that enriches the soul, though. I imagine that's why we haven't seen nations embrace this approach despite it becoming mechanically viable thanks to the log-in bonus.