Well the thing is this. If you dont pay any capital gains until you convert it to fiat, that is very easy. Because you could trade for a very long time and make profit but dont need to pay anything until you cash out. That makes it very simple to understand.
The issue is if you are suppose to count it every transaction, you have to convert the btc to usd amount at the point of sale? But how is that a 1k gain then if that 1k worth of btc could be 750 later on etc? So if someone made say 50k worth or profit doing many trades... let say all those btc profit add up 50k total on that day of the trade... if that 50k worth of btc is only 45000 now, then how can you even put 50k? Unless you turn it into fiat, it seem very complicated. If this trading was all in fiat, well thats simple. You add total profit and have a USD balance on the exchange. But everything is done with btc which makes everything not make sense.