Is the Ruger 375 dead you ask! - Was it ever alive. - me thinks it was stillborn!
Yep - That's my thinking, too.
Nothing wrong with most of the new cartridges Ruger has developed (or helped with rifles/hand guns) over the years.
Most haven't caught-on.
Off-the-cuff, I can think of only 1 that "HAS", but a long list of "HAS NOTs".