It seems you are unaware that you can purchase 2 additional retainers?
When they released this option as well in a recent interview they stated as to why it cost money. It was said in a recent interview that only 1/3 the player base even uses 80% of both retainers. As such they added the retainers you can buy with real money. In game currency does not pay for server repairs/upgrades/larger loads that's come from having these additional characters.