Why is it that billiard ball manipulators can juggle during their act and pop balls off their elbows, cups and ball workers can twirl their wands like drum sticks, coin guys can do a coin star and coin roll but everyone gets mad at card workers for doing comparable things?
This is a very common philosophy in card magic that goes back at least to Erdnase and his continued and persistent use of the word natural in The Expert at the Card Table. He insists in a card game that it is best to look no better or worse then the next punter when handling a deck of cards.
This naturalness was constantly preached by Vernon. To the effect that every motion made must be made in a natural manner and be perfectly motivated. Anything that you do outside of such could arouse suspicion.
For years the students of Vernon including Michael Ammar, John Carney, Ricky Jay and Juan Tamariz have preached the same. Economy of motion, naturalness and motivation has been the creed and mantra of most leading card men in the magic community for last hundred years or so.
The philosophy that it is best to avoid flourishing in card magic is still an idea that is very popular today. I remember listening to a recent interview with Johnny Thompson where he talked about the flourishes of Dan and Dave and how Vernon would have hated them. Johnny chooses not to do flourishes in his own act because of the Professor's teaching.
It is an idea that is very persistant today as well. Xavier Spade had a rant about the use of flourishing in magic a few months ago in Ellusionist's mini web series "Rewind".
It's surprising that you're not aware of this philosophy because I know you are a practitioner of mentalism. One of the biggest places where flourishes are avoided is in mentalism. Corrinda goes on and on about even avoiding ribbon spreads and fans in performance so that the spectator doesn't blame the miracle on your skill to handle cards but super natural means.