The article mentions that pinning is often used by mobile apps and IoT devices. In those contexts, you have an easy out-of-band mechanism to deliver the cert: baking it into the app/firmware binary. (The user generally receives this from the App Store, or in a cardboard box from a retailer, so no initial TLS connection to your server is required.)
If you're pinning the leaf certificate this way, really the only benefit I see of using a WebPKI cert is if you want to reuse the same API endpoint for a web app. Otherwise you're mostly getting a bunch of restrictions and downsides (information leaks from CT, revocation drama, etc) that don't make sense if the cert is hard coded in the client.
If you're pinning the leaf certificate this way, really the only benefit I see of using a WebPKI cert is if you want to reuse the same API endpoint for a web app. Otherwise you're mostly getting a bunch of restrictions and downsides (information leaks from CT, revocation drama, etc) that don't make sense if the cert is hard coded in the client.