It is not possible to give the reason for offboarding as it may tip off fraudsters on how they can evade detection next time. This is standard across the industry.
I note that if you know your way around the dark web, it's relatively straightforward to find a "financial crimes advocacy" website with suggestions on evading KYC and other compliance hurdles; obviously I won't repeat them here (and I know that probably the majority of would-be bank fraudsters probably aren't into checking the darkweb for advice) so I hope there's more to it than just information-control...