How much was the jackpot hit by your friend? I guess it was not that big, because if it was a huge amount then I think your friend will do the KYC. If he did not send the document means that the amount is still considered as low amount for him, but if he thinks that it worth enough then I'm sure he will do it to get the money.
At the moment, most gambling sites has terms that they have the right to ask for KYC. Although it is not mandatory but it can be asked for several cases like huge win, suspected as money laundering, etc. So basically big players who usually bet big amount and have the chance to win huge should be ready for KYC.
I do not like KYC as well but if there will be a time when a gambling site ask me for KYC because I win so huge amount, I will do it to get the money but I have to make sure first that the site is reliable and trusted.
He doesn't want to tell. Yeah, perhaps, it was not too big, but he only tells that the amount is enough to cover his daily life for 2 months. He just too afraid to send the document because he knows about the leaks of the document in the online store. He says that it still not worth to send the document to them although the win money can cover his daily life.
I don't like KYC either, and I always use the gambling site which doesn't use KYC. Besides that, I only a small player who want to gamble in my busy days without thinking about winning. But if somehow, I can win a huge amount, and the gambling site is legit, I will do the same as you.