I spent ten seconds thinking about the logistics of adding logging to the frontends, and...

Well, obviously I can't say for sure they don't have any. I didn't look it up, and if I had I wouldn't be able to tell you. But since I didn't, I can tell you that the concept seems completely infeasible. There's too much traffic, and nowhere to put them.

Besides that, not everything is legal to log. The frontends don't know what they're seeing, though; they're generic reverse proxies. So...