The original reason for wet streets was simply to keep dust, dirt and debris in check. Were talking dirt roads and such, its been going on since the invention of the moving picture. Now its mostly for dramatic visual and depth.
Im more surprised the discussion of day for night or even better, "its pitch black outside yet this is a lunch scene in a high school" subject wasnt first.
I want to know why in movies every sporting event, especially outdoors, seems to take place at night in an un-lit stadium ?
The football game from 'Last Boy Scout' comes to mind. It looked so dark you would have thought it was a pick-up game on a field with no lights but most football games I've been to it's so well lit it's brighter then regular sunlight in the middle of summer.
I was there for the Last Boyscout when they filmed the LA Coliseum scenes. They went over by a couple days, if memory serves, due to them flying the helicopter into and around the interior of the stadium with thousands of extras seated in the bleachers, which shut them down. Since they only had random masses to seat per day, lighting help mask this. In fact, when they pull up and Damn scratches the Roll's, thats a real soccer game going on in the stadium and real people walking around that exterior shot.
Im not 100% on this but I recall hearing they were not even permitted to film that day. The entire opening sequence and ending were shot on the same days. Those were real Raiders cheerleaders and the USC marching band. They had Paul Rodriguez and Mark Curry (Hangin with Mr Cooper) doing stand up for the crowd of extras.
One of the worst things about that film, and there were many, was the stuntman that bungeed off the scaffolding right at the moving helicopter blades yet in the film it looks like a stuffed dummy tossed at miniature blades forced perspective style. Not sure if thats a bigger crime than the dialogue though.