There is one difference, private servers do not need to make significant amount of profit to stay alive. WP is a company and its staff want acceptable salary up to the industry standards, private servers have less or no such problem at all. Being an official server iRO has contracts with kRO, they have to pay to run RO server and receive updates, while private servers do not pay kRO anything and use all contents for free(hence why they are illegal). They also have less control over what contents they can have, while private servers just take whatever they can from kRO updates without restrictions. You apparently have missed out this thread from a few months ago, and the reputation of private servers aint as good as you think. For the ppls who quit iRO, they are far more likely to end up playing another game, than on private servers.
yes i know about the reason our updates sucks, but still it could be fixed, if gravity wanted, but they don't so meh, let's keep gambling