Instagram, Linkedin, Tumblr...who's next?
They have gone crazy since they want to have their "consistent user experience"...
That's the thing, they just need to make the UX so badass that users will want to use your products instead of a 3rd party. Problem solved. Instead, they are just being lazy and squashing anyone who tries to innovate on their platform. Considering every feature on Twitter.com started on 3rd party clients, they're just shooting themselves in the foot.
But then again, that's assuming you believe it is about "consistent user experience", which I think it likely 5% of the real answer.
That's actually the public stock market. Private equity investors can vary anywhere from extremely patient, to being as impatient as public share holders. In Twitter's case, it's a 6-year old service that is peaking in valuation ($10 billion) unless it can find some new source of revenue growth, so I'd imagine the investors are getting a little ancy.