More seriously. I don't think that the issue is that Plone "does not get it right", but that simply nobody in Plone is really working on it.
Remember that Deco was already usable in 2011 when the editor was still competitive. (We did build simpler UI on top of blocks & tiles already in 2010.) Unfortunately, because Deco was "revolutionary" and not compatible with the existing Plone UI, not many seemed to adopt it.
Probably the main feature of Mosaic reboot for Deco was to make the composition compatible with all our legacy, to make it possible to start using it gradually. Rewrite for the editor was not a priority, because it could be done later.
And it could still be done. Thanks to our insanely flexible stack, there's plenty of options to start writing a more modern editor for Mosaic. For example, one could override the layout (editor) pattern while reusing all its configuration. Or keep the old and new at the same time by making a new widget for the new pattern (possibly inheriting Mosaic widget). Blocks / Deco / Mosaic layouts are still just HTML and use of server-side rendered schema-aware application tiles is fully optional.