It's part of most multifactor authentication systems, as has already been mentioned. You could get by with SMS-based MFA, but you really should not as it is demonstrably insecure. In the future, these other methods will likely just go away as well, as they should.
At some point during COVID, a lot of restaurants stopped giving you printed menus, and expect you to use a QR code to access a menu on the web. Some provide printed menus upon request, but I've been to places that just don't have them anymore.
Here's a personal one: On a road trip a while ago, I stopped at a gas station to buy a map, only to discover that they don't sell them. This blew my mind: growing up, this is just what you did when you were in a state far from home, and you could count on any gas station having a folded paper map of the state in it. I don't think you can count on being able to navigate that way anymore, so you'd either have to plan ahead and buy maps, or buy a dedicated GPS unit, or use a smart phone for navigation.
Later on that same road trip, I stopped in a small town and wanted to walk around for a bit. I discovered that all the parking spaces cost money (fine) but that there were no parking meters or kiosks to pay at. Just a sign with a QR code on it, presumably pointing to a website or app download where I had to pay. In theory I could have pulled my laptop out of my suitcase, connected it to wifi somehow (not via tethering, but maybe a nearby coffee shop or something), and used the webcam instead, but come on.
My insurance company offers a "service" where they track your driving via a smartphone app. This is an optional service, and naturally I told them to screw off. It is not hard to imagine, however, this becoming not-optional, or being penalized for not submitting to it in the future.
Oh, here's another one: my last employer bought me a smartphone on day one of my job there. Not avoidable. I did not stay at that job very long, but I don't think it's all that unusual for companies to just assume you're going to use a smartphone and be in touch with them.