Market was much less efficient in those days. Making money must have been easy for floor traders and MMs who could actually watch the floor brokers representing big money, and jump in along with their orders to scalp profits. And then you had a whole other layer to the game where whales like Livermore would trade off inside info, and manipulate prices to trap other players.
The basics of trading haven't changed, though. Much deeper electronic markets means edges are narrower and opportunities vanish more quickly, but you can throw far more size at them and get in and out with a click. Buy in a bull, sell in a bear, pay attention to general conditions and scalp moves created by big money.