App Store not offering previous version of app on old device

Dear Experts,

If a user with an older device tries to download an app, and the current version of the app requires an iOS version which their device does not support, the App Store will offer them an older most-recent-compatible version instead.

I've just had an enquiry from a user of my app for whom this has not worked. Specifically he has an iPad 2. He foolishly deleted my app from the device, and now the App Store will not let him re-install it.

Does anyone know why this may be? Is it simply that this App Store feature does not work for devices as old as the iPad 2?

Thanks.