Why should they? It works fine on the bog-standard industry charger.

That's a fair point if they actually do work fine on other chargers. My experience with previous wireless chargers was that they only actually worked if they were designed for the specific phone (e.g. Pixel 3 XL stand). Lots of going back and forth between charging and not charging and the phone itself getting really hot and not actually charging.

I fully accept that maybe my other chargers were cheap and crappy though, so maybe I'm just unlucky.

I've got a basic flat pad I bought from Amazon for like $15 that charges my iPhone XS and my Airpods quite happily.