Besides being a stepping-stone to the desire for full vertical control of the user experience Edge components are also integrated into other portions of Windows

Besides being a stepping-stone to the desire for full vertical control of the user experience Edge components are also integrated into other portions of Windows. This is similar to the situation with Internet Explorer. If I recall correctly UWP uses Edge's rendering engine (EdgeHTML) and JavaScript engine (Chakra). Edge integration/embeddability is also available to Win32/WPF/WinForms applications past a certain Windows 10 version. It makes some sense for them to develop something they have full control over if they use its technology in other core components/libraries of their operating system.