I don't think there are (still) a lot of people who bought 2019 mainly for the VSTi and never used BIAB previously.

The VSTi is a great idea, with a lot of potential, but in my opinion still need some work. For example, the ability of playing in sync with the host, following tempo changes, key signature changes etc. These features are standard in any VSTi I know, and people used to use modern DAWS expect that (and also a more modern GUI, btw) from any contemporary virtual instrument.

I'm pretty sure these features will eventually be added, and then BIAB VSTi will attract a lot of people, because despite is limitations, BIAB is really an incredibly powerful tool for any music producer.

PS: I've had many problems with previous versions of the VSTi, but with the last update is working OK on my system (I'm a Reaper user)

Latest BIAB version, latest build.