Well not to beat a dead horse, but...
Do professionals still (or have ever) use the F6? Haven't most of them gone digital? Those would be the fellas who would use and abuse their gear. Therefore, there would be fewer F6s on the market. Most F6 users would be serious hobbyists who are more careful with their gear. And, of course, the F6 is supposed to be more durably made too.
Now the F100s have been on the market longer and were around before digital took over. So there are more on the market that were "rode hard, and put up wet." I believe many F100 were used by professionals as a handier alternative to an F5.
But back to the OP, it looks like the control didn't fall off, it was broken off. The connection held - the plastic was snapped apart due to high stress. Even an F6 can have it's knobs torn off with enough force.