If anyone plays in scrambles, or corporate events or the like, then I'd bet none of those people walk 100% of the time.
I typically go to the course with the intent to walk just about every time I play, but I know there are rounds where that's either not possible, or it's just not something that would be desirable on a given day. If I'm playing with a client who likes to ride, I'll probably ride. If I play 36 holes, I may walk the first 18 and ride the second. But most of the time I walk, and nearly all of the time (except for the two or three rounds per year where I have a caddie), I drag my bag. Even in Chicago District events that allow carts, I usually prefer to walk.
I don't mind people who prefer to ride, and I certainly don't hold it against them.
There's probably only been one or two times where I thought it was just too hot to walk. Though in all honesty, I'm more likely to be open to riding on a cooler, wetter day than on a hot, dry day. Having grown up in Southern California, I'm not much of a mudder. And it's nice to have my clubs covered, as opposed to constantly fiddling with an umbrella, especially when it's wet AND windy.
One thing that bothers me about a lot of public courses that have been built recently is that they're designed around carts. Of course, as a source of revenue, it's not hard to see why. That's not to say the distances from greens to tees is exceptionally long (though they may be), but they're the types of places where you aren't going to find a bench very often. And on a long day, with a lot of waiting, it's nice to have a bench at a tee to sit at every now and then. Cog Hill #4 is pretty bad on this front. Granted, there's one greens fee that includes carts, so they probably aren't expecting a lot of walkers, but I typically walk when I play there. In addition to being one of the most difficult walking courses I've played, they stick all of the benches at the very back tees. This paragraph sounds pretty whiny, but it's a pet peeve of mine.