I think it has a bit to do with a combination of the new positional ranking system interacting with the standard beginning of season ranked chaos.
For starters the new lp protection that occurs during the initial placement games has incentivized some players in my games to not really care how it goes. I had a teammate literally say "whatever I'm in placements so doesn't mater." I like the lp protection in theory but it seems that there is the other side to it where people abuse the mechanic that is supposed to make placements less stressful, MORE stressful for other players.
Also I think that Riot has really pushed the idea of ranked much harder at the start of season 9 than they have done previously with things like the Awaken cinematic. Moreover, they have been targeting players that may have not been as into ranked previously and are highly encouraging players to play SPECIFICALLY at the start of s9, bringing many more players into the start of season fold.
While there's nothing wrong with players new to ranked as a whole, I do think a lot of players new to ranked exhibit a form of performance anxiety and may play much worse than they normally do in norms. This or they get tilted to infinity after a few placement games since they may think they deserve to be placed much higher.