That, plus the fact people were already poking into the closed firmware binary, plus the existence of an alternative firmware. By doing this, Polyend also kind of passes the responsibility of maintaining the Tracker devices to the community.

It's also worth mentioning that the release is not just a source code release, they added a lot of great features like sample streaming, and dedicated velocity and timing lanes. And they released APIs so that people can easily create new synth engines and effects.