TSQLT can be run by DBAs in support to ensure their support patches are not breaking known functionality.
TSQLT Does not require a IT:AD:Visual Studio license (even the free versions in large enterprises are not free).
TSQLT is Open source and does not run the risk of being removed from Visual Studio at some future date, putting at risk all testing efforts developed with it.
TSQL can be integrated with a Build server without requiring a Visual Studio license on the build server license.
* Considerations:
Average enterprise developers are more used to IT:AD:Visual Studio and may resist learning new tools.