You probably know that when you make a new team, for the first few matches you meet really low mmr teams (+- 1700-1800) yet when you win these teams still give you a decent mmr increase. This lasts only 3-4 matches and then you meet actuall teams from your own mmr.
BUT, did you also know that if you still have really low teamrating, and you play with another person who is also in the team but has not played yet, you again meet low mmr teams for again a few matches. You can continue this till around 1000 teamrating and then it won't work anymore, hence you remake the team and start it over.
Its a rinse and repeat proces and it takes some time and dedication till you have farmed up enough mmr to try for that glad/r1 push (Where you can get things like 2,7k with 30-35 winratio again).