Human brains are optimized for prediction of future events, because this helps with survival (eg: you can predict a winter coming up, so you stock up on food).

Randomness is by (some) definition unpredictable. But humans are so eager for pattern recognition that they will see, or expect, patterns that just are not there.

"Pareidolia is the tendency to interpret a vague stimulus as something known to the observer, such as seeing shapes in clouds, seeing faces in inanimate objects or abstract patterns, or hearing hidden messages in music." and also: https://en.wikipedia.org/wiki/Apophenia#Causes

On a similar note, humans are terrible at coming up with random/unpredictable sequences. If you ask a group of test subjects to pick a random number between 1 and 10, you get a huge edge when you guess 3 or 7.

I suspect it has to do with the same facilities that evoke magical thinking, and other pattern-event associative behavior. And like those pigeons in the famous experiment which were fed randomly and evolved various ritual-like behavior in association, we think we did something to achieve a win condition (or food condition). In the case of gambling, what we 'did' to win was gamble when 'the cards were hot'.