Why is there no 4-player pre-made group on Flex Queue? [closed]

Solution 1:

Four-man premades are disabled in Flex queue because a solo-player would have to fill the last position. The 4-man group would have peer-pressure and would be able to bully the solo player into picking a role they may not want. Because the solo player is the odd man out, they usually also end up as a scapegoat if things start going wrong in game, and the 4-man group harasses the solo player in retribution.

Another reason is that Flex queue is meant to be played in groups of more than one person. If 4-man groups were allowed, that would implicitly encourage solo-players to join Flex queue in order to fill those extra slots.