Because it is super fast to start trading cryptocurrencies with online trading brokers. In a matter of couple of hours you will have the ability to start buy and sell your cryptocurrencies, therefor making this option the best one when it comes to catch the current wave in order to try to profit from it.
The most basic way to profit from anything is to buy it cheap and sell in a higher price, therefor, making a profit. Alternatively, you can do the opposite, sell first when the price is high and buy it later when it become cheaper and again, make a profit.