It’s always about the money. Blazer probably has the higher profit margin (and it also happens to be sexier), so that’s the one you spend more marketing dollars on - just like the grocery stores putting the higher margin items where more eyes will see them.
The diesel on the Nox/Terrain was probably viewed as just an experimental option package. They probably didn’t make many to begin with, and it was easy to pull the plug on if sales didn’t materialize. Maybe it was partly dealer failure for not ordering and promoting them enough (because they themselves didn’t feel they’d sell in their markets)?
2011 Equinox 1LT (dlvd. Jan 2011): Summit White / 3.0 L V6 / FWD / Pioneer Stereo / 18" Wheels / 142k miles [01-FEB-2020]
2002 Impala 1LT (dlvd. Jun 2002): Summit White / 3.4 L V6 / FWD / Cassette-CD Combo /228k miles [01-FEB-2020]