T-Mobile, Sprint break off merger talks

This is currently true, but it does not need to be this way. Sprint is barely viable because of near-constant mismanagement for over a decade now.

There's nothing about the market at large that makes Sprint non-viable. There's plenty of customers and money in the US to support a strong 4th place provider. Sprint just refuses to execute anything properly (this was true both before and after SoftBank, despite the change in leadership).