why do they radically change the ball for every world cup? just to sell balls?

>>151082196
Yes

>>151082161
I think it's somewhat normal to hand out the unfinished ball to certain players in hopes of getting some feedback. Only Yamal or a specific team getting it would be bullshit, though
>>151082196
Yes. Not radically perhaps, since the 2010 Jabulani at least, but the balls have specific designs both in terms of looks and function. In the past, the World Cup balls were used as steps to drive the developments forward: balls became more uniform, smoother, more resistant to external factors. It happened because of how many parts a ball was made of and so on. The quality increased, and where better to show that than at the World Cup? Nowadays, they slightly differ within strictly regulated norms. They look different for marketing reasons.
And yes, it's about selling balls. Adidas has always been the official FIFA gear partner, they pay a lot for that and gain a lot in return