They spread popularity of a digital currency by selling people the convenience of it. It's kind of like how people can use their phone to pay for items in some stores without needing to swipe a debit/credit card or pull out cash. Eventually the people falling for it all will be those accepting implanted computer chips to make the process of checking out in a store easier. These likely would also be the people that would be ok with staying home and letting robots delivery everything they need to their home.

I use credit cards because good credit is needed so that I can have the option to buy a house since those are difficult to afford in cash. Other than that, I have no use for credit. Often times I'll spend just cash because I don't want my spending to be tracked. If you have an account with Walmart's website and have a card linked to that account, if you swipe that card at your local Walmart, your online account will show all of your purchases although you shopped in the local store.

They track everything. It's only a matter of time before places like Walmart will use facial recognition or whatever to track purchases even when paying with cash. Smaller stores are gradually being squeezed out by stores like Walmart which has been going on for decades.