Interesting, I do the opposite. When something is available in the Mac App Store or through other means, I will generally buy it in the App Store. Why? Application sandboxing is mandatory for Mac App Store apps and I strongly prefer that applications are sandboxed by default.
The second, less important, reason is that I can just install the applications with just one click and don't have to download them from different places, look up their serial numbers, etc.
That said, I‘m struggling with the constraints Apple puts on the business models of developers, for example when it comes to upgrade pricing. While I have a fair amount of software Mac/iOS subscriptions running (8 by my current count) there‘s definitely software I passed on because it moved to a subscription model.
In most cases it’s a valid reason - the app is malicious, poorly made or somehow in conflict with local law. Also imagine if you are an app developer an suddenly your project (on which you’ve spent countless hours of hard work) is unexpectedly leaked as freely available for download and side-loading. I’m not talking big Corps like epic and blizzard … but people like you and me.
Open source apps can be loaded easily, so developers who really want to make their stuff available can still do so and users won’t need to hack their phones to get such apps. But of course this can’t happen en masse.