Even that's not really true. Most software that ran on Windows 95 could be run without modification or even a single update on both Windows 98 and Windows ME. Even XP preserved compatibility for most programs, adding explicit compatibility modes you could enable for an application that wouldn't work out of the box.

So, in the old days, you paid often $50-500 for a piece of software and the developer would usually have zero burden to update the software for you. By the time the OS completely broke it, it would have been 5+ years later. All that time, the developer was freed up to build and sell whole other applications, or, to innovate new and compelling features to get you to pay the upgrade price to get a new version.

Today that developer would have to do 5 major updates with breaking API changes, and probably at least 1 full visual refresh just to keep up with Apple's changing design whims, just for that one app to not be bricked. They have less bandwidth then to build more apps, since each app carries its own annual burden of churn.