It's about viewership. Test match is BORING. I'd watch it, you'd watch it but maximum people will stay away. There is no point for BTV to show those matches as the sponsorship won't cover enough.
However, seeing that our boys still think an inning lasts around 70 overs or less in a 3/5 day game, BTV might be able to show the Bangladesh innings during the tour. It will only take a few more minutes then the highlights.