I don't know whether it's ridiculous or not, but it's definitely a culture clash.
Safari had a hard time attracting ports of other browsers' extensions even when you could distribute them for free and they were fully HTML-based. (Probably because there was no Windows version.) Now, not only do you have to pay, the old extension system has been deprecated in favor of a new system where you have to bundle your extension within a native app and implement a native-code-based interface. It's probably not a bad interface in isolation (haven't tried it myself), and makes it easier for existing native app developers to add extensions, but I expect it makes code reuse between extensions for Safari and other browsers quite difficult.
In comparison, both Firefox and Edge are going in the exact opposite direction and moving to an extension API directly based on, and largely compatible with, Chrome extensions. So pretty soon you'll be able to use popular extensions with any browser you prefer... except Safari.
But hey, at least now Safari will be able to take advantage of the popularity of building apps for the Mac App Store. Oh wait...