Bigger question: why isn't it built in to Google Calendar?
It’s called appointment schedule/slots.
https://support.google.com/calendar/answer/11608416
I love calendly because: 1) it checks my calendar for conflicts with a link or suggest times in gmail 2) adds zoom meeting details automatically 3) avoids having to do timezone math
I just send my calendly link and don’t have to discuss back and forth about who’s available when savings tonnes of time.
but it's not very featureful.