I wouldn’t assume that’s the only reason for how these apps exist. Most businesses pay considerably more for an app than it would cost to have a website. In some cases that’s due to something like robust offline support or tracking not allowed by the web security model but there are plenty of more common reasons: the owner wanted to be able to tell their friends that they’re in the App Store, they perceived it as more modern/cooler, they got a sales pitch about how this would boost revenue or customer loyalty, etc.

One way to guess about what’s happening is to look at the app quality and update history: if it looks like it launched in the original App Store round or has a hideous UX which is never improved, it’s probably not actually doing enough to be worth spending more money on.