What @HotKey saidIt's real money, real transactions.. not a "just for fun" thing. So they need accountability to protect against fraud, money laundering. It also provides a legal recourse for issues like non-payers.
Real information helps keep your account secure and gives you a leg to stand on should a problem arise. Look at it on the other side of the coin, imagine you did business on there with someone whom easily used a fake identity for buying or selling domains on the platform? It opens up avenues for using stolen or hacked payment methods to obtain goods.
Basically, yes it is necessary.