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.
for someone who already has bitcoin and wants to start altcoin trading, if they choose platforms that don't ask for verification it will be instant. you just sign up, make a deposit (which may take 20-30 minutes) and then start trading.
for someone who doesn't have bitcoin or wants to use platforms that ask for verification it is not fast at all. it can take days even weeks before some of these exchanges verify your account, then it will take time to deposit fiat to dump for bitcoin and then start trading.
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.
it is easier said than done.
what is low and what is high? you can never tell easily. you may sell thinking it is high and price goes higher, you may buy when you think it is low and price crashes further and when it comes to altcoins this becomes a pretty common thing.
