Fax is commonly used at least in the US because it has regulatory recognition as a secure means of transferring information, it’s highly interoperable, and it doesn’t really have a successor that has caused the network effect to die out entirely.
11% seems slightly higher than I’d expect, but not crazy. Contracts, medical records, interactions with the government are all good reasons to need to send or receive one occasionally. That about 1 in 10 households did last year? Makes some sense.
But how many of them do you think put it away within a week of using it to make content? I would bet the ratio of people who possess one to people who will be disappointed is huge, assuming there are in fact disappointed users.