Similarly, it's why iMessage gained wide adoption, became and stayed the de facto messaging app on iOS despite the users being able to go on the AppStore and download any other free cross platform messenger. It was already on their phones and it worked well enough not to push users to look elsewhere.
So if we can file an antitrust investigation in Microsoft for bundling Teams with Windows, why don't we also go after Apple for bundling iMessage with iOS under the same logic? Or after Google for monopolizing the web browser market with Chrome? Where does the buck stop on these ecosystems that have monopolies in their respective sectors?
We already went through something similar nearly 15 years ago when Windows copies sold in EU would not come with IE preinstalled but would prompt you to choose which of the 4 major browsers at the time (IE, FF, Chrome, Opera) you would like installed (while now those same browsers would be FF and 3 flavors of Chrome, how ironic). Was a good idea at the time that needs updated and refreshed for modern platforms and tools, not just Teams.