$1 won't get you Linux ISOs up to modern display standards. Great if that works for you but the high end is more like $20+ (emphasis on the +, taxes and shipping not included) per Linux ISO so its understanding why many might prefer sharing them digitally. And that's before getting into cases where the Linux ISO vendors don't even want to give you the specific version you want.
Did you see the 'thrift store' part of his comment? I do the same thing as him, and depending on the location around town, an ISO on a DVD can be as little as 50 cents, and a modern Linux ISO on bluray, including 4K (though rare I see those) are rarely over maybe $3.
Yeah, garage sales are another place. you can get multiple for a buck :)
Especially those "one package wonder" ISO vendors, $20 is steep.