Also consider that the strongest PSA 9s/10s from the 2 cert era or earlier are likely locked away in collections and will not see the light of day for some time. In comparison, almost every 6 cert or 7 cert card will be seen in auction, listed as a BIN, or “flexed” on social media.
This is an example of sampling bias where prospective buyers disproportionately see the less desirable older certs, while the “weaker” newer certs are overshadowed by the “stronger” copies from the same era. It creates a false narrative that the older certs are inherently weaker, but it may be that the stronger copies are just not available for purchase.