Basically, in league's ranked system, it becomes a brick wall to try and rank up. How would you guess that MMR is calculated? At the very minimum amount it would be based on wins, so lets take a look at how you progress in ranked.
**
LP Gains: Say you earn 10 LP per won game, minus 10 for each lost. You start with 0. You gain 100LP to rank up. From here, you need to win Provisionals, which is best of 3 or 5. Essentially, you are 10 games positive on your W/L, which increased your MMR by a lot. Now, you need to win 2 additional games (or 3). Since your MMR is now higher, you're being paired against stronger opponents, or you're being paired against MMR teams of a total amount equal to your team. Which means, based on LUCK, you're either getting paired with 4 players of your MMR on your team vs 5 players of your MMR on the opposing team.**
Or, what happens nine times out of ten, you're being paired against players with a lower MMR than you, but your allies all have even lower MMR than them, but the MMR between teams equals out because of your high MMR values.
So you lose your Provisionals. Say you win one game, lose your next two. Now you are currently at 9 games positive on your W/L. How do you get back to Provisionals? Win a game. This puts you back at 10 positive W/L. Which puts you right back in the same boat. In the end, it puts you in an RNG grindfest against a brick wall, that has the potential to be broken with raw skill, but most likely will not.
Theoretically, the only way to lower your W/L ratio/MMR while still keeping at the same rank would be to lose your first 2 (or 3) Provisional games to get booted back down to qualifiers. From there, win one back into your provisonals, and you're now at +9 instead of +10, which could be rinsed and repeated until you're actually negative in your W/L ratio/MMR, which will eventually happen to you if you're continually throwing yourself at the provisional grindwall. The only way to counteract this would be to make Provisionals not count towards MMR... Which could have a negative or positive impact on the game, it would be damning for players who are up to a very positive W/L ratio but it would not impact players who have a negative W/L ratio.
Essentially, because of the MMR system, the only way to rank up is to either;
A: Play like a damned god to go from Silver 3 to Silver 2
B: Lose certain games to decrease your W/L (MMR)
A being unavailable to many players who are good, but don't have the capacity or likening to playing top-tier heavy carry champions, while B is considered "Trolling" and will most likely get you in trouble.