> Also, because third party app developers largely align with Apple's philosophy, less and less 3rd party software even works on my computers anymore.

I think it's more about 3rd party app developers attempting to improve their products and stay relevant.

If Apple releases a new framework or API that would make a developer’s app better, but it requires macOS 14 or later, are they not supposed to incorporate it?

I've noticed lots of 3rd party developers keep older versions of their apps available for older macOS versions.

On both macOS and iOS it is straightforward to target older devices while using the newer SDKs, and to use those new frameworks conditionally based on the user's OS. Of course, Apple's tooling makes this harder and harder to do, the older the targeted OS is.