In a normal gumball, you'd have equal chances of getting the blue and the red. Most of the cases, the manufacturer even does the gumballs all the same flavor, just different colors, because they KNOW that if you put a more desirable flavor people will try and take the flavor they want. With all the same flavors, even if you like a gumball that is the color blue, you would be "eh, that's okay. I have a gumball anyway" and go on with your life.
What we see right now with gachas, is that you'd have a machine with 70% red gumballs that taste like rotten fish, 29% blue gumballs that are Ok At Best and will last you like 10 seconds of chewing, and 1% that is The Perfect Golden Gumball.
There are few creators that really use the Gumball Analogy on their gacha machines, and I can recite them by head. But listen, I've seen gachas that you HAD to have ALL the items for the gacha to work properly, INCLUDING THE RARE. I've seen gachas that you would roll L$75 and had the chance to win A SINGLE PANTY ITEM. How is that fair to the consumer? How would you "desire" a trash item that you don't want in your inventory? Some people will roll, and roll, and roll until they get what they want. There are people that spend hundreds of dollars in gachas because they see the value in it. How is that not gambling??