Probably precisely why it isn't really enforced- you shouldn't do it, but they're not going to waste resource to go out & actively look for it.

They'd have to log IP for that account, and then scan through all the people who plundered it (assuming they even log that information, which I doubt), if that same person is using that account & being plundered by another account that also has that IP, then technically you could say "He's feeding his main".

It can get complicated though, how do you know that's not his brother on the same connection- what constitutes as actually feeding another player? Is the act of feeding a player illegal? What if I just actively plunder the same person everyday because we play at the same time? Is he feeding me? How do you know if it's intentional or not?

It's something you just can't really enforce & it being illegal is probably a formality.

Of course I can see this thread getting deleted quick.

Huh, I never thought about that- from this whole thread that's probably the one thing with alts that'd I'd actively agree with as being broken.

Someone before mentioned that higher powers don't benefit from plundering alts- but they do, a lot of people hate being plundered, people have told me that it's infuriating losing coupons- it's actively a very negative thing to lose something that means so much. I'd prefer it to be that you lost the "Coin" side of it, the plunderer still gets his coupons & the plundered still gained his coupons, but coupons weren't deducted for losing.
Some high Battle powers on my server make a choice NOT to actually plunder people, while others plunder alts- I actually don't see a problem with it from this view point as it avoids actively annoying the player base.

I've even known & seen people actively change guild to a guild that has stronger members purely based on them not wanting to get plundered- it's a very strange mechanic to have in a game.