There are carefully crafted rules to make things like in-game winnings and frequent flyer mile accruals non-taxable. I think the key rule is that you can't convert the in-game currency to real cash; this is why airlines close your frequent flyer account if you sell miles or offer to give other people your awards for money. They probably don't care, but the IRS does.

How this all changed with cryptocurrency, I don't know.

I think taxes are all about what's written down and what logically makes sense. If you pay someone $1000 to do a job, they have to pay taxes on that. If you invite your friends over and spend $1000 on food that they eat, they don't have to pay taxes on that. I don't know why.