> a clean, fully featured tabbed terminal, included in Windows

You'd either get a Microsoft Word equivalent of a console window in that case, since everyone has a different set of features they consider essential, or the Notepad equivalent (more likely). A tool's value doesn't necessarily increase with more features and features are never cheap (in Windows, at least, where there are documentation, translation, configuration, group policy, and other concerns).

Tabbed console windows exist as 3rd-party applications already, seemingly with minor problems for one user or another, but I'd argue those problems are easier to rectify than for MS to develop yet another alternative that people grumble about even more because it doesn't contain their own personal pet feature.