The Roadster (2008) used a different connector than the Model S (2012) and is completely incompatible. JS1772 (2009) was already being adopted as a standard by cars like the Nissan Leaf (2010) before Tesla's current connector was being used.
Tesla's Supercharger network at the launch of the Model S was a total of 6 chargers: https://web.archive.org/web/20121124081536/http://www.teslam... . So the initial infrastructure investment was not that significant.
Further reading into that article though you can see the Superchargers were capable of delivering 90kW. JS1772 cars were limited to ~20kW L2 charging at the time which is why Chademo (2010-ish) connectors were included for faster charging on earlier EVs. CCS (2013) would become the unifying replacement that added faster charging to JS1772.
More on topic, the rest of the industry and world has moved on and standardized to CCS. No one should start using Tesla's connector on their cars now. But making an adapter to use Tesla chargers on a CCS car could make sense. But having yet another thing to lug around in the car won't be ideal. The obvious logical choice is for Tesla to start retrofitting Superchargers with CCS now that it's open and eventually ween Tesla owners into using adapters that Tesla already makes.