No clue how many people didn't renew, but my guess is that renewals this year were significantly lower than they've been any other year in the last decade.
Similar to what dogfrog touched on, I think the largest population of people that didn't renew were likely moderate to fair weather fans that had simply renewed every year out of habit and a sense of obligation. Last year gave many of those people an excuse to take a break from attending games, and sadly, they probably enjoyed the benefits that came from it: more money in their pockets, more flexibility and free time on their fall saturdays to relax, get chores done, and drag the kids around to their sports/activities, the comfort and convenience of watching at home and getting to flip between games and eat their own food and drink their own drinks. Add in a team that's been boring, frustrating, and uninspiring the past few seasons and you have a recipe for a lot of people that decided to opt out again this year.
