And what of the thousands that went to Orthodoxy? Is that also staggering?
Frankly the largest number of people who leave any and all of the movements, aside from those who simply disappear into the ether of secular apathy, leave their movements for independent, unaffiliated communities. The institutional Judaism of movements is on the way out, like I said.
Your list of reasons may be reasons you left Conservative Judaism, but I sincerely doubt they describe why any significant number of other people have migrated leftward from Conservative or Orthodox Judaism. The majority of people, both within the Conservative movement and outside it, that I have seen drift away from traditional observance almost all share the hallmarks of severe lack of Jewish education, and/or secularizing apathy, and/or some sort of selfish motivation, like intermarrying. I could probably count on one hand (with fingers left over) the number of people I have ever met who began as Orthodox or Conservative, had good traditional educations, were not intermarried, were interested in remaining participatory and observant in some way, but chose to become Reform for philosophical and theological reasons.