The steemit delegations are removed on a per fraction basis as a user powers up. Earn 2 steem? You now have a 13 sp delegation.
My brother's account also showed me that they are removed for inactivity and 'snap back' when that person becomes active again. Much of what you say about delegation is based on assumptions that my experience are not true. I monitor the users to which I delegate, though not as efficiently as steemit inc.
Your point that is should be 50 and not 15 is interesting, and in my opinion they should use 15 to reach out and get 50. Check out @gtg's comment here.
Money talks, but in some senses steem is more democratic than anyplace off chain. Every SP counts. Its important to understand what steem is before we complain, that it is not something else.