I could think of 2 reasons
- Customization, more features than the default. For example you can rename apps, change icons of apps, organize your apps to categories etc. Something not possible with the default launchers. Yes, other 3rd party support these, but if you already use some Microsoft products like Onedrive, Outlook etc, Microsoft launcher could be a logical option. They already spy you, so...
- You are a Microsoft 365 subscriber.
They will. If Apple doesn't comply with EU Digital Markets Act (DMA) they will have to pay fines of up to 10% of a company's global turnover for infringements. Let them try not to comply lol. Their deadline is on May 2024.