Would anyone know why matchmaking is how it is?

Where, if you lose enough games in a row, you start playing with people 1-2 divisions lower than you? It doesn't really make sense to me. Just makes it harder to climb if you hit a stream of bad luck in games that throws you down a few divisions and kills your mmr. What if someone played on your acc without you knowing and dips your mmr? I gotta play with low golds as a Plat..? Yes, the enemy also gets the people that are low division, but chances are if you're consistently good, you'll get the weaker spectrum of players, which effectively makes it a 1v5-9. Especially at the brink of plat, where there's a large variance of players that are A actually plat, B boosted, or C the lower division people that are stuck in elo hell cause they can't improve enough to crawl out (or are hitting bad luck themselves).

Even in terms of the other way it goes, where you fight higher division/mmr people if you win enough games in a row...Is that supposed combat smurfing? Cause if smurfs managed to get Challenger, Master, even high Diamond...They can definitely do it again on their smurfs. Especially since their placements will very likely place them in high gold/low plat (if that's still possible) so they get most of the work cut out for them. And especially since solo/duoQ is still enabled until Diamond, where skill becomes very known. And since diamond+ is only 1-2% of all players, does smurfing really matter? Otherwise, there's no point to fighting higher division people, because, as you climb, you enter higher divisions and will fight higher division people anyway. So you fight higher people ontop of higher people...???

Just, why?