I don't find that they do.
The things that make cash useful for money laundering and black market purchases also make it easy for me to quickly, and without unnecessary ceremony, drop a few dollars in a tip jar, give some money to a panhandler, split the bill at a restaurant, chip in to an office gift pool, pay my kids an allowance, envelope budget, buy ice cream from an ice cream truck, etc. etc. etc.
Bitcoin in particular fails miserably at these sorts of use cases because nobody wants to sit around waiting 10 minutes for a transaction to confirm over a $2 soft serve.
Crypto in general fail because they're complicated and fiddly to work with. This creates way, way too much friction these sorts of casual transactions, and effectively shuts out people who aren't technically sophisticated enough to feel comfortable messing around with this stuff.
That isn't to say that crypto doesn't work as a store of wealth. But, as a circulating, everyday currency, it seems to be stuck in the same situation that Linux on the Desktop has been for the past couple decades: for a variety of reasons, some of them very good and no real fault of its own, per se, the community just doesn't seem to be capable of sorting out the UX.