There are many. We have an online supermarket with an app (Picnic) who don't support iPad, don't support landscape, don't support dark mode, etc.

I bet it's due to product managers not caring about those.

Because despite Apple having clear guidelines a huge number of developers think their 'custom UI' is what customers really want. When they don't. The best apps use system components and follow the HIG. Always have, always will. Your custom tab bar is stupid.