Simple question: When you hear people talking about sports stadiums, they sometimes refer to the seating area as the ‘stands’. Why **‘stands’ ** when they are sitting?
It dates from a time when people did stand? (WAG)
Short for grandstand. I think the “stand” refers to the structure itself- a raised platform on which things are placed is called a stand- witness stand, bandstand, bedstand.
Why are they also called bleachers? I’ve never seen anything being bleached in them.
There’s no roof, so if you sit there you get bleached by the sun?
For the same reason you park on the driveway, and drive on the parkway. 
Because people used to stand there. I think standing areas were abolished after the Hillsborough disaster.
In the UK, yeah. I doubt more than a handful of Americans ever heard about Hillsborough, and I doubt further that it would have had much effect on US stadium design. AFAIK, even professional stadia built over here in the '30s usually didn’t have standing room.
While we’re being annoying…why do theaters advertise “Stadium seating” while the luxury boxes at stadiums advertise “theater seating?”
People there stand to sing a standza* of The Star Spangled Banner about some guy named Homer D. Brave. In the bleachers, you gather with other cheapskates to bleat yer (bleacher) complaints about the quality of play. George Will wrote that, in olden times, stadiums would sell standee tickets on the field in the area where pitchers warmed up. Fans milled around “like bulls in a pen.”
*Yeah, I know.
The fans would also express concern for the viewing conditions afforded Hispanic attendees in the bleachers: Jose, can you see?