That’s true, but this happens because usually 95% of people are always on the latest version a few months after the new version was released. For developers, it’s really not worth supporting older versions when the overwhelming majority of users already upgraded.
Still, many large companies still support older versions when the user base is very huge. I work for a huge bank and we had to support all the way to iOS 10. Only this year it was recently upped to iOS 14, which now covers probably 99.99% of users.