It has nothing to do with a lack of capability of the older machine. They just decided it wasn't worth the effort to support the model of wifi chipset present in the older models, effectively killing them off.
I think you may be projecting. Wifi cards go bad. It happens. Sometimes they can be replaced. Sometimes not. I've had it happen to lots of my machines over the last two decades.
But I don't think it's fair to characterize what could very well be a hardware fault as the work of some bean counter in Cupertino sitting behind his desk rubbing his hands with glee.
I can't find reference here, but I remember a discussion with an Apple engineer who said that AirDrop had been blocked in a certain model, "due to incompatible wifi", but that the wifi card mentioned was not one they'd ever heard of being put in a production Mac, i.e. "ass-covering BS".
Even Apple doesn’t have unlimited resources. They may still offer patches for outdated WiFi cards in a future update but it’s silly to commit to doing so in your initial OS release.
But I don't think it's fair to characterize what could very well be a hardware fault as the work of some bean counter in Cupertino sitting behind his desk rubbing his hands with glee.