How does the number of blades in a fan affect the flux of air? I read that 3 blades are the best option but some companies uses more blades because there's a misconception among people that more blades generates more air.
3 blades would be indeed close to optimum for power efficiency and require less material during manufacturing.
But typical engineering goal for fans is different: maximum performance / noise. More blades $\implies$ slower rotation for same performance $\implies$ less turbulence $\implies$ less noise.
Also, check out my older relevant question: Wind generators - why so few blades?
You have to balance competing issues, so it's an optimization problem.
Yes, more blades move more air, but also cost more power. (Like in a small aircraft, each propeller blade can't consume more than about 100 hp.)
If the air is moved through a smaller diameter fan, then it has to move at higher velocity (to get the same overall flow), and power goes as the square of velocity.