Simply put, because
Borat is a fictional character. And I believe you told us it isn't your real name. If someone wants to use a "pen name", that is ok. It just has to send real and not be announced that it is a fake name.
Some people do have names that sound fake. Bear Bibeault is one. However, we showed us Bear really is his name.
Companies have rules. Websites have rules. Learning how to accept that is a job skill. Why not practice here and pretend you like or accept the policy?