It's a double standard for a reason. Teen boys are horny as fuck and starved for pussy. A hot female teacher fucking him is doing him a solid. If that happened to me I would be fucking ecstatic.
It's still wrong obviously, but it's not the same as the other examples that you cited.
It's like someone stealing your wallet but returning it to you with an extra thousand dollars in it. Sure, they committed a crime by stealing your wallet, but are you really mad about it in the end?