duaneiac,
I've often thought the same about the Argo/Cadet catalog. It's been woefully under-served in terms of digital reissues, particularly in the US and Europe. A quick scroll through the Argo/Cadet discography shows many artists who recorded for the label whose recordings have been overlooked. These are all in addition to the three that you mentioned -- Ahmad Jamal, Ray Bryant, and Ramsey Lewis. Consider ...
Dorothy Ashby - Several
Kenny Burrell - The Tender Gender
Lou Donaldson - Several
Art Farmer, Benny Golson, and the Jazztet - Several (not counting the Mosaic set, of course)
Bunky Green - Several
Al Grey - Several
Barry Harris Trio - Breakin' It Up
Willis Jackson - Several
Illinois Jacquet - Several
Budd Johnson - Several
Hank Jones, Kenny Burrell, Milt Hinton, Elvin Jones - Here's Love
Harold Land - The Peacemaker
Jack McDuff - Several (including one of his very best records, The Heatin' System)
James Moody - Many (an egregious oversight, IMO)
Shirley Scott - Several
Sonny Stitt - Many (no surprise there)
Baby Face Willette - Mo' Rock and Behind the 8 Ball
I'm know there are others that I'm missing.
I suppose someone at some point decided that mining the Argo/Cadet catalog for reissues wasn't worth it from a dollars-and-cents point of view. But I know that decision often had little or nothing to do with the quality of the music.