Even things like HDDs that don’t become “obsolete” in 18-24 months get sold with plenty of life left (unplanned downtime is more expensive than new hardware), but obsolescence makes it happen even sooner.

Regardless of who owns it or what they do with it, those GPUs will get sold on the used market with plenty of life left. Older AI GPUs, networking equipment (eg 100GbE), SAS drives, etc have been easy to find on eBay and other sites for a long time, because data centers replace hardware long before it’s expected to fail.

12gbps could be useful if you use port expanders to put dozens of drives on the same port, but without a port expander you’re right you wouldn’t saturate the 6gbps channel.