Statement by Garmin:
Garmin has instituted a new policy regarding the accessibility of our developer programs. The previous strategy of freely available APIs quickly became unsustainable due to increasingly high demand. In response, we have established a new pathway for our Connect API. Firstly, there is a vetting process. We are strategically limiting the scope of this program to specific developers that will enhance the user experience. Secondly, those who are approved for inclusion will be charged one-time $5,000 administrative fee to cover the extensive engineering and server support required for the Connect program.
Working in the industry for more than a decade I can say that Strava has an API done right. It is hosted on Github, allows free access for every developer, sets a rate limit for every app and charges only for usage over the rate limit.
https://strava.github.io/api/
It can be that easy!