Individual hosts decide. Same as how I can no longer visit httpS://chase.com on my ancient PC that doesn't support HTTPS, let alone a modern web renderer. Chase

Individual hosts decide. Same as how I can no longer visit httpS://chase.com on my ancient PC that doesn't support HTTPS, let alone a modern web renderer. Chase has left it behind. ISPs also decide; they turn off their cgnats and start handing out /48s etc, at the latest when the cost of leasing /32s addresses exceeds the cost of being incompatible with a tiny few straggling hosts.