Did you take the time to ask those friends why they quit? Because I also have a big friend list that is 95% offline PERMANENTLY. I talk with the ones I have close to me, and they said that they quit the game, because of the toxicity, not the game play. I will bet that most of your friends also quit because of that.
Also, we're talking about professional scene and players, and high level streamers, not your random soloQ friends. Your randoms and my randoms quit the game for various reasons. Some of them might do it because they genuinely do not enjoy the game anymore, some of them might be pissed at the game state, others quit because of toxicity, and others quit for real life reasons. I don't see how this is relevant to what I said.
Back to my point, it's only NA streamers and pro players who quit the game, or talk bad about how it's dying etc. Do you know why? Because they are not good enough to be successful at it. Look at Shipthur. The guy doesn't really care about soloQ anymore, he just plays for fun, joking with qtpie about how he hit diamond or w/e. Do you know why he doesn't care? Because he gave it a shot to become a pro player, achieved nothing at it, and now he just doesn't care. Qtpie is the same, as are so many other ex-pros. Like it or not, those are the unsuccessful players that tried and failed. The regional successful players are still playing the game regularly. Bjergsen, who has had a lot of success in NA still plays passionately. Same for Jensen, DL etc. Same for EU players.