Control and from there perhaps more money.
I would leave their system and also many others.
Yes, but what if there are only about 100k of such people?
Restriction might be a requirement of special licence.
This would effectively remove ability to execute arbitrary code from most of the users.
The ones who want to run arbitrary code or develop software will have to pay. If someone complains about this, they would be told to shut up and would be explained how this is actually a benefit for majority of the users.
Anyway, I will stop here.
Edit: I think that Apple is not doing it only because it is not their focus at the moment.
The special licence you are talking about actually exists. You can sign your Mac apps with a certificate and it will not ask a user if you want to open it, but this is not restrictive at all. This is actually a benefit because nobody can modify your app so if they would force this, I wouldn't mind. Most of apps that I use are signed anyway.