Why would BTC gains be subject to self-employment tax? Surely they would be treated like other forex gains? Honestly if I had $10 million in BTC gains I'd get

Why would BTC gains be subject to self-employment tax? Surely they would be treated like other forex gains? Honestly if I had $10 million in BTC gains I'd get a tax professional and seek a private letter ruling from the IRS to clarify the situation. I imagine that misreporting $10 million of income would be an unpleasant experience.