Earlier quoted context omitted.
Probably because G Workspace is comically cheap.
The whole industry of calendar scheduling boggles my mind. It seems Google/Microsoft consider them small fish to fry, but Calendly is a multi-billion dollar company
Even then Outlook does have FindTime and has a plugin system to let you use third party tools like Calendly. There's also a product called Microsoft Bookings that's more of a direct competitor to Calendly. But at the end of the day Calendly's revenue is estimated at around $100 million from what I could find online and that's a drop in the bucket for Microsoft or Google.