Comment by TeMPOraL

Because they don't accept their website is not worth an app. Most of that long tail of businesses has a transactional relationship with users, who by very nature would ideally want to think about them as little as possible and only for the short moment of actual transaction.

In short: I do install apps of main platforms and physical shops I frequent. It's usually vastly better than a website, even if it just wraps a webview. But I don't want to install an app for every site I visit, for the same reason I don't want to go on a date with every stranger that smiles at me when I pass them by on the street.