It is a fact (and no speculation) that bike (drivers) or car (drivers) take the round-about counter-clockwise. I don't mean that the rules are made for bikes or cars, I didn't try to say from where the rules come from. In this way each country for sure has its own historical excuses to do so. Nothing to do with the question. Now about the question: Why is track cycling done counter-clockwise? Because the rulers wrote it like this. Why did they do so? I try to guess, yes, I am not inside of the ruler's head and in the rules you cannot find any rule-justification, just the rule itself.

Sorry but when I posted my answer (yes, LEGS) there was no mention at all on the other proposed answers.

Right, it should be... be carefull in all situations until you get the new tires!

@Carel is a great idea in the context Kilisi explained. Having an accident is never a good idea, no matter the context ;)

I do not imply they are equivalent. Numbers are different... and both measures are commonly used nowadays.

@Kilisi swapping the tires is a great idea!