I suspect this statement isn't true for all Linux distributions, but it really wouldn't surprise me if distributions backed by large companies (Red Hat, Canonical) or base distributions that large companies rely on (Debian) kept packages around for a very long time to satisfy corporate customers.Why in Linux the last state that works does have everything included including the packages ? Can't FreeBSD do the same ?
FreeBSD doesn't have the backing of a huge company. Sure some large companies use FreeBSD, and some contribute. But given how mature the Ports framework is, and how easy the tooling is to build your own packages, I'm not sure how important recent packages are to large donors let alone very old packages.
I'd wager that the people that care about very old packages and don't maintain their own package repository are unlikely to donate a significant sum of money for FreeBSD to maintain the amount of disk space to store old packages, or maintain ageing technology (e.g. maintain certificates in a manor that is secure while being compatible with old versions of pkg(8) or imagine if pkg(8) switched from HTTPS to something else, the old HTTPS delivery mechanism would need to be maintained).