The baseband is the device that manages radios on a phone and is typically powered by a closed source driver (potentially due to federal/government restrictions). See:
I am in two minds about this.
On one hand, I totally agree. There is a huge library of Android software out there that immediately adds value to a new phone platform. Users want the games, and apps like Uber, Lyft, Skype, etc.
On the other hand, (a) those apps will potentially run inconsistently on the device due to the apps looking and operating differently to the base platform, and (b) the business is always at risk of Google killing the ability for them to run those apps, so opens up a significant risk vector.
This is the catch 22 situation. We want the dynamic catalogue of apps, but we are supporting a closed ecosystem. This is one of the major reasons why other phone platforms (e.g. Ubuntu and Sailfish) have struggled.