The point of deprecations is to eventually force a bad experience for those who are not keeping up. They definitely do work, but the time periods to affect change can be long. In the tech sphere many seem to interpret a long transition period as not working granted the usual pace of change.
That's different. There are ways in which ipv4 is subjectively better than ipv6, and "the catastrophe of needing more addresses" has not really panned out yet.
Resolver software is massively distributed, you don't force anything. The only place that can force anything from the top may be root servers, but even then, many resolver operators are probably just downloading root zone in bulk via https from somewhere to precache it and don't contact root servers at all.