However, it staggers the imagination to call Glocks "lowest common denominator" ... just doesn't make sense given their popularity with a whole range of people who have sufficient experience to know better, and who get to choose whatever they want.
But in a sense, they ARE the lowest common denominator.
Glocks are, by far, the most common striker-fired polymer pistols out there. Most folks (even LEOs, who may or may not actually know a whole lot about firearms) know what a Glock is.
They are (relatively) inexpensive, reliable, easy to find, and parts and sccessories are readily available. They aren't really the best striker-fired polymer pistols out there anymore, but many folks don't really care. Buying a Glock doesn't take a lot of thought. You just plop down your money and know you are getting a good, reliable, proven pistol that a lot of other people have been happy with.