[derivativethrow]

To give you an answer focused on the crypto itself, because the way they explained the TLS properties doesn't make this clear:

1. Integrity is redundant with authentication, so really you could say they're ensuring confidentiality + authentication. You can't authenticate a thing without implicitly obtaining assurance of integrity. It's a strictly stronger property.

2. Confidentiality is (usually) insecure and unreliable without authentication. Without authentication you have no PKI for a key exchange to symmetric encryption, so you can't even do TLS in the first place. And if you don't have a carefully applied MAC or a native AEAD mode, your symmetric mode isn't that secure either.

So really what you're asking reduces to the question of why they need the most sophisticated TLS scheme for encrypting their streams. If they want the most secure TLS scheme for confidentiality, TLS 1.3 is the way to do it. They explained one particular facet of why this is the case, re: perfect forward secrecy.