I think this is likely to be what I saw others mention on earlier posts. Lots of enterprise or business software that hooks into the control panel.
So even if Microsoft does migrate all the Windows options over to settings there’s still going to be software that uses control panel to manage their own settings.
Unless Microsoft is going to make it possible to hook into the new settings app just as easily then they’re going to have to keep the old one around even though they keep crippling it.