I'm a volunteer here so I don't know for sure, but here's my guess:  They're obligated to offer to hide your heart rate because that's considered medical info, and subject to privacy rights.  Cadence info is one of a few items that can be used as proof that a cyclist actually earned a KOM, so we all want to see that to detect cheating.  

that kinda makes sense! Thanks for the good answer! In my current case I lost my cadence sensor and found it again on the way back 😂😂 It had been overrun by cars several times but still worked. Naturally, my cadence for this ride is complete bonkers.