WTH, why can't I simply register a helper to a device?

For example, my phone, reports battery level via the HA companion App.

I added a helper to record the discharge/charge rate to document how the battery performs over time.

Same for things like my air quality sensor, I use helpers (good job on the UI for this, love you guys) to add additional metrics for analysis.

But why can’t I add these metrics directly to devices and see them when I search my device in the Devices & Services page?

Closing as a duplicate of Wth can't I add a helper to a existing device?