Why do it,because there is long-term investing,mining or the possibility to do other business,including offline?
I believe that when you trade or invest, it's always accompanied by a new learning just as these two things. So, if you are an investor, then in the long run you will have to learn about trading. And if you are a simple trader then you'll get to learn more about investing.
We're not stagnant and we're going to learn more things in finance such as the crypto market and these things of investing and trading. If you are going to ask why trading and not the others? because we've got the basics of it as buy and sell.