Given that they're specifically saying you shouldn't use it as a sports watch, what use is an HRM, especially when compared to the utility of a compass and barometer/altimeter?
If I recall correctly, the original Pebble had a Compass (which may not have even been used until a OS overhaul later on) but the Pebble 2 SE didn't. (https://www.reddit.com/r/pebble/comments/4kz7ch/why_pebble_i...)
The https://www.whoop.com/, for example, doesn't even have GPS. All of its value comes from its HRM.
Barometer is especially niche and not something very trustworthy outside of devices made for it. To the average person, compass is only useful for showing orientation on a map.
It muddies what would otherwise an easy upsell/upgrade.