Automatic overview dashboard: how does HA decide on which sensors to show?

I can create a dashboard, add my own cards etc. But I’d like to understand how Home Assistant works.

I added the Fitbit integration. I have 1 device and 37 entities. Here’s what HA shows on the dashboard:

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Why did it decide to show only these 5 sensors? And why if I hide Calories, it will only show 4 and not pick up a 5th one like the Activity Calories:
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