The reason is because it’s new - there’s no clear winner for what’s the best, and not getting the standard right would likely mean the downfall of EVs. CCS is looking good and Europe has effectively forced it upon manufacturers, though.
The Chademo and Us CCS plugs are terrible. Objectively bad (expensive, heavy, etc).
The European CCS plug isn’t quite as good as Tesla’s but is probably good enough.
The Us should adopt either Tesla’s plug or the European plug.
Also, CCS wanted to reuse some of the pins from the L1/L2 J1772 plug, but the original plug didn’t have room for larger pins. Tesla’s plug was designed from the beginning to be eventually capable of fast charging.