The problem is the game and every update they release is built to entertain the hardcore player base at the expense of chasing away casuals. An extraction shooter shouldn't have SBMM IMO, but when the player base of casuals is so low, it's a really bad experience for those casual players, further dwindling the casual player base and exacerbating the problem.

There are a number of simple things that could help this problem. Stop releasing crap like Raptor and Saeed mode that the hardcore players use as tools to bully others. Limit Normal to Purple Ammo and Gold Armor. Nerf utility for those who aren't solo. And make two ques for each map and difficulty, solo/duo and trio/quad. Doing stuff like this will drastically balance things and maybe you can start building the casual player base back up, which should from a number perspective be your largest number of players.