The different settings apps that claim to manage the same thing don't cover the same settings. The old apps are not still there to support users who don't like the new look, they're there because the new apps are insufficient and cover an overlapping but different set of configuration. It's thoroughly confusing and frankly a terrible design choice.

Another reason why old control panes still alive is that new settings app isn't customizable by 3rd parties. Some 3rd party drivers added custom configuration panel on control panel and old drivers remain forever on windows world.

That would be more believable if they let you do the same things. It would probably be more accurate to say they had to keep the old one because the new one is (still!) missing half the settings.