Nirosu sparkles already mentioned this but most of the people you mentioned donated real life money for their "millionaire" status adding "taxes" wouldn't only hurt everyone on the server with in-game money loss it would be plain highway robbery for the donators (they pay real money for in-game money and then we take that away i.e. we steal their money) secondly it makes it impossible to save up for let's say a beacon or nether star since they're so expensive. 3rdly where would this money go? you want to forcibly flush money into a dark hole? turn it all over to jack for "the greater good"?