> so backwards compatibility is neccessary.

True, but from a technical perspective "necessity" might be a bit of a strong term. For example as far as I know there aren't any Windows versions left that don't have support for TLS 1.2 but are still supported (i.e. not EOL). iirc Windows Server 2012 has support, but it's not enabled by default. So that's the closest to "unsupported" you get with Windows.

I think this is mostly because people are some what hesitant of enabling TLS 1.3. Because merely enabling TLS 1.3 along side TLS 1.2 can trigger latent bugs in clients.