Good point, hadn't considered it may be the developers of whatsapp who are reticent to provide access to others to access their infrastructure.I think it's more down to WhatsApp.
WhatsApp have been clamping down on third party access and don't yet have an app that lets you use the service from multiple places like Telegram or Viber do; they really are a bit slow on the service improvement front.
Allowing synchronisation of messages to a car system is probably a long way down their list of things to do.
I wonder if web.whatsapp.com works in the browser? Will test later.