What it comes down to I think is that historically, on average, stock traders come out ahead while "gamblers" do not. (Of course you can still go all-in on one company, or buy insane options, or use leverage, etc., and thereby gamble on stocks.)

Investors come out ahead, not traders. The more "trading" it is (meaning more short term), the more like gambling it is. There's even a point where you go from positive to negative sum.