A tiny fraction of Twitter users use third-party apps. So put yourself in the shoes of a bean counter…

"We can't serve ads. We can't sell a subscription. The API costs money. If we kill the clients we lose a few users, but some will stick around."

It makes sense on a spreadsheet, but misses the users' value. They produce the content that brings you to Twitter.

Killing clients is exactly what you expect from people who just don't get social networks, and too arrogant to listen to those who do.