I get it. We don’t like the “door slams”, urging us to download an app before we can actually use the website. Unfortunately, they seem to be effective or they wouldn’t be doing it. Sometimes, “business” decisions come first, no matter how much they affect immediate usability.
It would be great if they just used Apple’s “Smart App Banner” (or a similar display on other mobile devices), which displays details of a specified app on the App Store at the top of the page and doesn’t block access to the website.