These companies are competitors. There was a time when it was worth the user/developer goodwill to let other networks build their graph off of Twitter's. At this stage (and it's been this way for a while), Tumblr almost feels like a migration path away from Twitter since it allows for longer content. If users can replace platforms but not graphs, what is stopping them? Twitter recognizes this and wants to stem that. It might not be what we expect from a web or (former) API company, but I don't think it's personal. They're just transitioning away from being an API company.
It seems like to get popular you have to be open and then to make money you have to be closed.
It seems like to get popular you have to be open and then to make money you have to be closed.