Yes, it’s strange. My idea here is: for distances both things are typical: meters and kilometers. Every day we need to handle both unites. It would be impractical to give longer distances in meters (“Hey Jeff, it’s still around 100000000000000000 picometers to your home, will be there in roughly 4200000000000 nanoseconds…”).

But even huge distances on Earth can be measured in km, and we don’t need megameters.

With calories however for all practical purposes we have a number range in which it is okay to use kcal. So here people just forgot that the k actually has a meaning. It makes not much sense to go down to the level of cal.