It could be a cost issue. A chip that collects data from connected sensors and sends it via Wifi is small and cheap. Adding a display and buttons ads size, complexitiy and costs. Therefore manufacturers offload the interface to an app and a device you already own, and they can update without expensive recalls.

If the task or device is more complicated and the device would also need it's own storage, CPU, display, sound etc. the product costs could go up by hundreds of dollars, depending on functionality and how many units they plan to ship.

I also hate apps. Still have my 2010 smartphone in a drawer that still turns on, however it;s useless because google playstore, maps and email now used an more modern SSL standard that this phone does not support anymore, and it won't receive any updates. I expect the same will happen to a lot of devices that are controlled by apps when the manufacturer decides he won't support it anymore, or Google breaks the app because some new protocol must be supported now that didn't exist 2 years ago when the app came out.