It's probably in the same vein as how phone apps that need a new feature quickly may decide to simply start a WebView.
I think their efforts to make their own browser-based controls feel like native controls was what proved thst Microsoft did actually want the web control for convenience.
Sadly, these days that native feel is hard to come by. UI toolkits are now super complex and the "solution" seems to be to port the entire UI toolkit to a Javascript runtime, then not maintain that for a while and let it deviate from the native standard, and launch a new Javascript runtime to make up for it. Updating anything in the OS has become easy, so you don't need to design give years ahead. In two years, you can just roll out an update and change the look and feel of the built-in applications.
Their browser was kind of shit when it came to sticking with preexisting standards, but if it weren't for their XmlHttpRequest, who knows what the web may look like. Their security disaster of a browser helped advance the web, not to build an ecosystem or bring possibilities, but to keep their monopoly.
IE's webviews saved a lot of developers from having to write or purchase a bespoke input parsing/formatting/(de)serializing formats whenever rich media features were required. It standardised the API in a way that allowed all developers to assume support was present, similar to the way DirectX could be assumed to either be present already or be a quick install away on any recent GPU in a time when every GPU manufacturer developed their own bespoke GPU API. Plus, Microsoft was already known for its backwards compatibility for developers (well, unless you were an early web developer, I guess).
Firefox showed that the inclusion in the OS doesn't mean Microsoft gets to have a monopoly if the competition is good enough. Then Chrome came and ate Firefox's lunch.
Microsoft's mistake was probably that they were so blatant about everything. They did things because they wanted a monopoly, and weren't afraid to tell others. Google dresses themselves in lies and deceit calling everything "open" and claim they want to "advance the ecosystem" when their true goal is to hold an iron grip on the internet and the devices connecting to it. Anyone who thinks operating system vendors like Apple and Google aren't at least as evil as 2000's Microsoft has fallen for their tricks. Even Linux has this control issue; just look at IBM/Red Hat trying to prevent people from switching to alternatives, or Oracle anything.