Then they would have to remove the various hooks in the Settings app that actually call and open the Control Panel.
How many are there? I can think of several (advanced mouse settings, advanced network settings, printer properties, date & time has a callout back to the old panel..)
Windows 10 came out nine years ago, so they don't seem in any particular rush.
Well, that button probably dates from the late 80s or early 90s, when Apple was comparing Macs to branded IBM PS/2s and such that were sold to schools and enterprises.
And they weren't wrong, at the time. Those PS/2s were fuckin' expensive.