It's just the media companies desperately holding on to old sources of revenue instead of trying out new licensing models.
Or it's because exclusivity pays.
I mean, I'm sure they'd love to have worldwide distribution - it's less people to deal with and less people means less middlemen taking profits.
The problem is, the old distributorship model pays quite well - they know if they get exclusivity they can get a lot of money from it, so they pay a lot to the studios.
The problem is if you want to break exclusivity, then the amount they're going to pay you for the content is a lot lower. And that difference is not made up by the additional providers you bring in.
The problem is exclusivity pays a lot more, and the exclusive partners are willing to fight for it.
Take Bell (Canada) for example - the CRTC ruled they can no longer "simsub" (a practice that's really only desirable during US election season) - basically if a Canadian channel is showing the same content as a US channel, then providers (satellite, cable) are required to substitute the Canadian's channel content over the US channel.
Well, as an experiment, the CRTC ruled that simsubbing the superbowl was not going to happen starting in 2017. Bell was upset, being the exclusive distributor for it in Canada (because 95% of Canadians have cable or satellite) and the simsub rules meant anyone turning to NBC would get Bell's version (with Canadian ads).
Personally, I think simsub is just bad policy - it was designed to help CanCon, but I think it really goes against it because it's more profitable for a channel to simsub by airing the same programming as the US than to air Canadian content instead which results in the Canadian content being quite marginalized (until the US picks it up).
Bell is spending millions in lawsuits to overturn this one experiment. Bell spent 20 years in court getting people to not install US satellite dishes in Canada, too (Dish and DirecTV are *illegal* in Canada, even if you pay for them and not use hacked cards or anything!).
Oh yeah, and the Bell CEO speaks out against VPNs, calling them "thieves" for using it to watch US Netflix. She even called her daughter a thief for doing that.
That's the kind of money on the line - and the studios and networks go along with it because there is so much money being thrown around that non-exclusive distributorship would simply make a lot less money.