You are talking as if all people can make a native app with the same knowledge and amount of effort as it would take to develop a website.
Sometimes, web developers would want to go further with their app and deliever "native" functionality. Sometimes, a person wants to build an app but only happens to know how to build a website.
It's a much more complicated matter than just some idiots deciding "let's build an utterly pointless thing and then let other idiots build horrific fiji-mermaid-esque hybrids!!".
https://asylum.madhouse-project.org/blog/2018/10/26/Walking-in-my-shoes/