The difference is a slot machine is mathematically negative expectation. Also Bitcoin is zero sum after commissions. So very different.
If tomorrow the USA gets together with China and Russia and persuades the entire world to outlaw Bitcoin, with the threat of a heavy punishment for anyone trading in Bitcoin, the value of Bitcoin will crash, probably very close to 0. In this scenario (which is not all that far-fetched) absolutely everyone loses, hence not a zero sum market.
If you and I agree that we each own a million fake dollars, we don't actually lose anything when later we decide we aren't.