So it makes more sense that in those instances Stake is more strict on their requirements compared to the verification a small gambler needs to pass.
KYC verification for higher level gamblers makes sense for obvious reasons, but asking op to provide his source of funds doesn't really make much sense. Deeming mining as the only legal source of crypto income makes things worse.
Why they consider mining could be that you have your mining equipment which cost much already and you Will continue to mine irrespective of the bear or bull of the market.
What the heck are you talking about? So many miners end up joining/quitting due to bull/bear market which is why what you stated makes zero sense.