As I left work yesterday, my boss saw me suiting up into my mesh jacket and textile over-pants (yes, they have a mesh strip, but it is almost worthless.) He almost immediately asked the question I have heard from just about everyone I work with, "Don't you get hot in all that stuff?" He followed this one up with a variation on the same theme, "Why not just wear a t-shirt?" My standard answer to that type of question is a little silly and trite: My skin might not be the best out there, but I'd like to keep it nonetheless. Obviously, there is more to it than that, but it is a simple and fast answer that most people can accept as "good" reasoning.
I would, however, like to expand on that a bit here. Hot weather gear seems to be a bit of a paradox. If you want protection, you need to wear full gear. The more clothes you have on, the warmer you will be. In hot weather, wear fewer/lighter items of clothing to keep cool. How do all of those fit together? You see the apparent conflict between the first and last statement, I assume. The solution is mesh gear. It is not as abrasion resistant as textile or leather, however it will hold body armor in place and it still holds up better than denim. Also, it lets air through to your skin as well as blocking your body from direct sunlight, both of which keep your core temperature lower. So, as you can tell, proper attire can do more in the way of protection and comfort than most people would guess.
One word of caution, mesh can get very chilly. This morning it was 67° F as I rode in to work. That's not a terribly chilly temperature, however, at highway speeds it can get on the cool side and when you ride through a patch of fog you get instant motorcycle air conditioning.