I think there’s two schools of thought, and both are just as valid. The first is Dagosa’s. The second is “everyone has a cell phone now. If you have a flat, you can summon help. You don’t carry spare batteries or alternators or radiator hoses. Why carry a spare tire?”
Regarding the statistic cited in OP, that statistic was provided on a user-edited answer site by “ID1072286662,” who both asked and answered that question, and who has no other posting activity except for a rephrased version of the same question, which he also answered. The data is therefore inherently suspect. I would frankly be surprised if it was that high, as statistically that’s nearly a flat tire per person per year once you eliminate children and elderly-who-no-longer-drive.
I don’t remember the last time any friends or family had a flat tire. The last time I had a flat tire was in high school, and even that was only caused because some jackass slashed a bunch of tires in the parking lot that day. Technically, that spare tire IS just excess weight, because I never use it.