That's exactly my point. It was first based on a miscalculation. When they realized that, they switched to a more accurate but still incorrect definition. They have gone through multiple iterations, each more accurate than the last, but none that are nice and round.

Actually, if there wasn't so much politics (and fake science) involved, there are plenty of things they could have used from the get-go that would have been nice and round.

The "nice round" figure that you offer from the speed of light, and suggest that they would have used had they known it then, is not nice and round and it is not related (and therefore would not have been used).