The reason you're stuck is because you've been lied to about how far you can expect to progress.

If you spend any time in this subreddit at all, you've very definitely heard a claim along these lines:

Any decent player can easily get at least Diamond in this game

I've seen some variation of this claim dozens and dozens of times. I've seen someone with a lot of play time get widely mocked as an outright failure because they were still in Platinum in S1. It seems as though the prevailing community sentiment is: average players can easily get to Diamond rank.

If you're unable to do so, you're bad at the game.

In reality, even if you exclude Bronze 3 in its entirety, only the top 20% of players made it to Diamond last season. If you're looking at Season 1, being Diamond rank right now means you're in the top 4.8% of players.

I will stress again: this calculation only includes players who are Bronze 2 and above. It absolutely does not include idle accounts, people who never played ranked, or even people who tried to progress past Bronze 3 and failed. For the purposes of this calculation, Bronze 2 is the lowest rank.

These completely fictional claims of how easy it is to get Diamond rank are generating a ton of toxicity as average or even significantly above average players get hard stuck (as expected!) in metal ranks. Those players have internalized the notion that not being able to get to Diamond rank means that you're unredeemable trash, even though that rank actually represents the top quintile at best. Those players then look for some reason why they're stuck in "low elo trash tier", and pretty much the only answer available to land on besides yourself.... is your teammates.

The mathematical reality is this: the progression that an average player can expect from last season is high Gold or low Platinum. That's the level that more than 50% of players that made it to Bronze 2 were able to progress to. That is the level that a 'decent' player can expect to achieve with some time investment. The players in Diamond are quite a ways beyond 'decent'. They are quite good.

If you're looking at Season 1, the average player can expect to be high Silver or low Gold.

There's nothing wrong with being average at a video game. There's certainly nothing wrong with "only" being in the second highest quintile at a video game. These are not things to be ashamed of.

You're not "bad". Your teammates are not "bad". You're just average, and that's ok. If you want to be above average, seek advice and practice, but also understand that the curve you've been sold is so wildly skewed by online commenters that don't know any better themselves that it's undermining your ability to just relax and enjoy the game.