The reason you can't send stuff to your alt is because you can't friendlist your alt. They did this to make "chain of custody" on duped items or RMT stuff easier to track. They also made it so you can't friendlist someone offline so players don't have to clear a hojillion friend requests from spammers (or just creepy people) every time they log on.
It's not a direct "you can't send stuff to your alt because RMT," it's a side effect from other attempts to get around common issues. One that they're not motivated to change because...well, people who have mules but not access to FC storage chests are in the minority.
Shared storage is a possibility in the future, especially with personal housing, but again the motivation just doesn't seem to be there for the time being