Calories are one of the worst ye olde units and it's honestly surprising they made it this far, being used day-to-day even in places where most of those got deprecated alongside various imperial and local systems by the SI (metric) system.

They are so old and confusing that it's actually impossible without further context to tell if someone saying "calories" means actual calories (cal) or "food calories" or kilocalories (kcal), since at some point in the past dumbasses began reading "kcal" as "calories" and it stuck.

The SI system has joules (J) and kilojoules (kJ), the latter of which is perfect for replacing kcal for day-to day use and is written on EU-compliant food stickers alongside kcal. Yet calories still carry on the inertia of "everyone is already using it".

This didn't stop us from deprecating literal feet with metres, yet it's surprisingly effective for calories, which don't even offer the convenience factor of being comparable to an everyday object.

Why? Is it because contrary to metres nobody outside of physics is ever bothered with their relation to other units?