How has the number of people I'm following decreased this past week?
Banning and member passed away doesnt impact your following count, you're still following them. John Burgess passed away last year, Im still following him. Most likely they just quietly dropped you. Go to the profile page of your followers, youll see the gray following you tag. If you block someone and unblock them immediately, that would remove them from your followers. Basically people do this when they dont want someone to keep interacting with their content. The dropped followers can still see their content from time to time in their feed, just a lot less, since the following status is removed.