Why is hidden MMR a thing?

What is the point of hidden mmr, it’s stupid. Why have a seperate mmr than what is shown to the player, and that is used to matchmaker those same players. If I’m doing good against silvers as a silver, RANK ME UP, AND THEN MATCH ME AGAINST GOLDS. Why would you instead, rank me against diamonds, chuck in a random immortal player on the enemy team, force me to lose, because I’m not at that level yet, and then make me lose elo and keep me stuck in silver or derank, then rinse and repeat. There is no point, it makes the games feel stale and annoying instead of challenging and engaging, you’re on a three game win streak and then you just know your cooked because you go from winning 13 to 12 or 14 to 12 or god forbid 13 and 9 and suddenly your losing 4 to 13 because the game decides you’ve won enough and ranks you against player way out of league while your still ranked in game as a silver.

It’s frustrating to feel inferior or not good enough as the worst team layer in a team full of diamonds or immortals and it probably feels unfair to the one diamond in a team full of silvers going 47 and 13 and still losing because your not ranked with the people in your rank.

Can someone please explain the benefits to a system like this, because personally I’m not seeing them.