It looks like it they wanted to use their existing special field management keys (field advance and field backspace) with tab being a different user experience. [0] Document does even use the word "Tab". "Field Backspace" seems to duplicate "Home" key usage under some conditions.
To be fair, Microsoft & Bill Gates are bad at quality user experience. "Ctrl+F" differs through their applications.
[0] https://archive.org/details/bitsavers_ibm525xGA2onDisplaySys...
*Edited.
The more I think of it the current TAB (SHIFT+TAB) key should of been used for entry navigation navigation only while the white space tab should of been something such as "SHIFT+SPACE".
"To be fair, Microsoft & Bill Gates are bad at quality user experience."
In some ways. Gates deserves never-ending enmity for plaguing us with backslashes in paths. But in others, Microsoft advanced the state of UI and UX more than anyone else in the '90s.
"Would of?"
Not sure the case that the parent refers to, but there's a good reason that CTRL-F in the Win95/Exchange Mail client and Outlook will invoke the Forward email message command.
It goes back to what is the common action that the user would perform in the app. Forwarding an email is more common that Finding text in an email - at least to Billg.
see https://devblogs.microsoft.com/oldnewthing/20140715-00/?p=50...