Nowadays most enterprise and bespoke intranet apps are targeting Chrome as a platform, not "the web". It's a re-run of the IE6 situation in the late 90s / early 2000s, except this time Microsoft is the victim, not the beneficiary.

Whereas it used to be that big IT departments would nix the installation of any 3rd party browser, nowadays almost all accept the use of Chrome. And if you're selling an app into a big company, you always tell them to use Chrome, and never advertise IE/Edge support except as a last resort.

If Microsoft want to sell their cloud services into these companies, they need to support Chrome-based apps. Edge won't do. As such, they have little choice but to fork it and build their own browser, tied into their services. I'm sure they recognise the potential problems and downsides, but consider it the least worst option at this point.