I agree with you from the developer point of view. I had this argument with the store owner - i lost XD. The store is already performing well, theme is clean and responsive. They just want something different.
Marketing wise, there is something to gain. Big chain fashion stores seem to believe it also - Bershka, Zara, Pull&Bear, Jack & Jones, ... they also have a freaking app.
I think its because there's low noise in push notification marketing compared to email.
On the other side, making an webview app is easy and fast nowadays and some websites are asking crazy prices for automated app creation, like < $500. Companies maybe pushing this to their customers for easy profit.