so why checking a root certificate if you proceed anyway?

It's not nessecarily for root checks but rather considering that new attestation formats may come around and can't verify for that reason but it is allowed to not send an attestation (i have actually sites reject my solo with attestation but accept it when i told my browser to not send the attestation, lol) to just be treated as not having an attestation.

Also pulling an attestation is not always for enforcing certain security keys or anything, but it can help example identify models and tell users about security issues or updates for their devices, or to help users keep the devices apart easier by telling them what kind of device wach one is.