Hey, this is due to your friends having little or no recent matches played in the gamemode you are playing together with. The mmr was reset with the addition of bots and until the hidden mmr is high enough you will have to play matches that have a low amount of players in them. This is to do with the game seeing your teammates as new players because they have no mmr score and need to build it up.
Matches in the higher mmr tier no longer have the minimum of 20 bots in them. This was removed some time ago and bots only fill up the empty player spots after certain time period is over and the game is about to start.