Even with that bottom roster focus there are only so many players that can be active on game day.
While coaching plays a role, methinks it's the lack of speed and want to of the immediate backups that are active that's the main issue on coverage teams.
For example: This offseason I pointed out how I couldn't believe that Jaylen McCollough had the 2nd highest snaps on special teams last year, but ONLY had 5 special teams tackles (3 solo, 2 assisted) for the season.
Not much has changed this year. If the website I'm looking at is correct, so far this year he has 1 through the first 7 games. From that I can only assume that teams are either running away from him all the time or he simply doesn't want to play special teams.