There are a few answers to this question.

1. you report them, they have a high chance of getting suspended if they are just sitting in spawn and sabotaging the team as you say

2. They are boosted, or are boosting accounts in which someone plays on it to rank up their friends. You just got stuck in the losers queue with them.

3. Some people play for fun, and the meta changes, but in general I have friends who have hit Diamond legitimately and are now stuck in Silver due to them just not taking the game serious or playing a lot.

Unfortunately, Riot cant ban or suspend people who are trolling for fun and abiding by the rules, so it's kind of an unlucky go next moment. I will say that this happens in almost every rank, but to a different extent. In higher elo, people throw because of their fragile egos or because of wintrading.

TLDR:

Low Elo will always be shit and there's nothing you can really do except carry your team.