There isn’t only one reason for limiting max online accounts, there is a million reasons and if i had the choice i would set it to 1 account per ip.
There is alot of stuff you can do with multiple accounts logged in at the same time that wouldn’t be possible with just one account. There is also the simple reason Darkjedi mention about having one money maker on all the time, some people would probably have all three accounts making money at some point. Or just having a “bitch” character to run around and buy your main character stuff that it needs to train.
Small stuff like this impact the game alot, if we wanted people to be able to make money super easy we wouldn’t lower the sell prices on stuff. Everything we do we do for a reason, even if it’s making life abit harder for you guys. 🙂