Since they are putting big money on that particular site, it means they trust the site. Therefore, undergoing KYC should not be a big problem for them as it's just easy to complete it. These big-time gamblers are not dumb to just trust a site with their money easily.
These big gamblers' research is beyond average compared to the majority and they are very strict at choosing a site.
KYC is not really a problem if there's a time that it will be a mandatory thing to do. We have no choice in the first place if it's become a necessary requirement. Just make sure to just comply with it on a trustworthy site and of course, not with the site that just comes out of nowhere and lacks reviews.
Well, I respect those who can provide, that was their choice, and all we have a choice either. But I was expecting this to become mandatory in the near future for security purposes.