I feel like this gets suggested regularly and am frankly surprised this still isn't a thing.
It really kills my mood for a match to have to miss the live due to life getting in the way and then being told straight up before watching the game that my preferred team lost the match. This is even worst because this is essentially the movie staff telling me how the movie ends right before buying my ticket. It's not my friend just casually dropping that they lost, it's you guys, Riot, that just goes "Yeah we wanted you live so screw you".
Make it an option if you really need to. Maybe some people prefer knowing before hand if a match is worth watching (ex: "Oh what X team won?!"), maybe some just don't care, whatever, cool. But there really isn't any reason not to have the option.