I think part of it depends on family size too.
I cook a decent amount. I actually enjoy it, however I've found that when I buy ingredients for a meal I'm looking at either eating the same thing for several days in a row or throwing out enough of it that it would have been cheaper for me to go out for dinner (ie, buying a whole bag of hamburger buns and then using one and throwing the rest out isn't very cost effective).
For more complex recipes I still enjoy the process but it's not uncommon to go to the store with a list of stuff I need to get for one meal and the total come up to $30 or more. Sure I've got enough to make a meal that would feed a half-dozen people, but half the stuff will go bad before I'll need to use it again.
Just from the financial aspect (not the health), it's far less convincing for a single person to cook unless they truly like it or they want to do it for the health benefits.