The RJ is a premium product. The airlines just don't charge a "premium" for it.
I can see it now:
[picture of spiffy RJ on a jetway with pax getting on, everyone smiling and laughing, sun shining] "Annoucing new ALL JET service to XYZ! Come one, come all, book your tickets on our fast, quiet, and safe JET AIRCRAFT!! A $1 upgrade applies."
[picture of Colgan 1900 sitting on the ramp in State College, PA while passengers walk in 3 foot deep snow drifts in a blizzard] "OR you could fly on our Beechcraft 1900, a slighly used prop-JET for $1 less!"
Yep, people would save a $1 wherever they can. Even in the "good old days" money was still an object. I wonder if there were ever studies done showing if people would pick an RJ over a 1900 or DHC8 if it cost $XX more, etc. I bet not!