'Just breaking it' in the case of these shell enhancers would result in the user having no user interface whatsoever after the upgrade.

Windows' upgrade process could in theory disable the shell extension, but that would be even worse than uninstalling the program given how programs on Windows do not take kindly to being 'half-installed' (case in point: uninstallers that break when some application files are removed).

This is what backwards compatibility leads to, and there is no way all parties can win in this scenario.