I was afraid that was the case. Microsoft just can't do anything right these days - their solutions always seems to bring more disappointment than satisfaction. They could've easily just let us pin the buttons wherever we wanted, but I guess giving everyone an option to customize the (overpriced) software to their liking is asking too much.
Up until Word 2007 you could put buttons anywhere on a page. Microsoft got huge complaints from corporate IT departments about the headaches this caused them. They scaled back on how easily users could make changes to the user interface. The QAT was the one concession to user customization. With Word 2010 they implemented allowing limited changes to the Ribbon tabs.
Modifying the Quick Access Toolbar (QAT) in Microsoft Word
For some time, the "New Experience" (now called Visual Refresh Preview) did park these icons in the Title Bar. That has changed, I'm not sure when.
Note that each of these functions has a built-in keyboard shortcut. (Ctrl+S, Ctrl+Z, Ctrl+Y)
The only time I use the Undo button is when I want to go back in the Undo stack using the dropdown and undo a number of actions. (Usually after running a macro that didn't quite work.)
If you want to get a message to Microsoft, this user-to-user support forum is not the place to do it. They do not see anything you post here. Instead, use the Feedback mechanisms.
Giving Feedback on Microsoft Word or other Microsoft Products