"All cars" is absolutely not true. If I drive up to a Tesla Supercharger with my Mach E in the US, I'd have no way to charge my car. The Tesla charger has a proprietary plug that needs a proprietary app with a proprietary payment network to start the charge.

Tesla chargers are not open, in the slightest. Them publishing specs online on the physical plug design doesn't make it open to everyone. There's still lots of Tesla IP that covers those specs and designs. Tesla won't license it to other automakers unless other automakers essentially never enforce any of their IP.