Why is the icloud adress limited to 21 characters?

My name was already taken and the same happened me at gmail. My solution was to add my middle name and the result was an address 23 characters long. That was no problem with gmail but icloud seems to have a 21 characters limit, why?

This will probably keep me from aquiring an icloud email address becuase adding something similar to my real name will only result in confusion with the already taken address. Adding my middle name would make some sense but anything else would feel too contrived.

I would really like to be able to use applications like Notes and maybe even mail but not if I can't be able to choose an email address that makes sense so please explain to me why I should be prevented from selecting an address 23 characters long...

Ps. I really love my Apple products (iMac, Mac Book Pro, iPads and iPhones) but I don't like them being locked into services that doesen't make sense to me. It is quite frankly taking the edge off the so called user experience. Stupidity like allowing 21 characters for miljons of users to come up with unique user names...