Twitter will provide the primary mainstream consumer client experience on phones, computers, and other devices by which millions of people access Twitter content (tweets, trends, profiles, etc.), and send tweets. If there are too many ways to use Twitter that are inconsistent with one another, we risk diffusing the user experience. [...]
As we point out above, we need to move to a less fragmented world, where every user can experience Twitter in a consistent way. This is already happening organically – the number and market share of consumer client apps that are not owned or operated by Twitter has been shrinking. According to our data, 90% of active Twitter users use official Twitter apps on a monthly basis.
After gaining popularity in large part due to 3rd party clients built on the API that Twitter built for that purpose, Twitter is now changing directions and basically telling 3rd party client developers to go away.
Nice.