But they don't always release a next gen device. And a lot of people who own a <brand> device will automatically buy next gen <brand> when it comes out. And then only a comparatively small fraction of games is typically re-sold without modification.

You think the return on the tiny percentage intersection of those conditions justifices the cost to society in terms of wasted materials and labour to do that? Does it even justify the manufacturer's development costs to create that lockout in the first place..?