From a player prospective, why does riot balance mostly around ranked play?

Obviously there needs to be some consideration for ranked when making balance changes, but i mean is it damaging the experience for players by being riot's primary concern?

When you think about someone who plays the game from a ranked prospective vs someone who plays it from an entertainment prospective. If there is a difference in the skill of players in a game, then a competitive scene naturally forms. The competitive players which want to get better and rank higher will play what ever offers them the best chance of doing so. If that means the effective champion pool is only 40 champions at any rank higher than bronze, then so be it. Most will pick the champions which are mathematically the best option, even though at most ranks comfort/experience with a champion is more important than the champion's power.

Yet from an entertainment prospective, playing against the same champions over and over again, because they were balanced around ranked play and not normals, diminishes entertainment value. Yasuo and Lee Sin are good examples of this, the is a massive disparity between their ranked and unranked play rates, and they also tended to be the targets of the most frustration on the boards. Yet they are by no means "OP" when talking about ranked balance. Lee Falls off late, and yasuo is countered by saving an extra exhaust and/or any of a number of tanks. Playing against the same champion isn't necessarily going to be fun the 100th time around, yet it can be balanced. This holds true for any champion, and if it was ranked it'd be met with their counter being picked just as often, if not more often, but we don't see this. I think it's a fair assessment that in normals players are more concerned with their own picks than they are with the opponent's. Where as in ranked, there is equal importance applied to both team's champion picks.

I've seriously got to wonder if this will/has harm(ed) the game in the long term. When the game's balance is made on the assumption that players will care about their opponent's picks when selecting their champion, then wouldn't an environment which players are not privy to that information, or don't care to consider it, unlikely to be balanced?

There is the obvious answer, that viewers of esports want to see more champion variety, even though the players don't really care and will just pick which ever champions are best. Though i'm not a sports viewer so I really can't speak in depth on the topic, but i'd think it'd be similar to physical sports, where the roles might be the same (champions in this case), but the different players are the ones which keep it entertaining and each match different.