In the U.S., ... classification of bitcoin as property. Thus spending bitcoin is a taxable event and capital gains may be owed. Therefore, many would rather just not use bitcoin for spending.

Otherwise, there needs to be the ability to earn in bitcoin. Right now, workers need to ask (or insist) to receive some (or all) of their pay in bitcoin. There are just a tiny fraction of organizations that pay in bitcoin, today. So that's one component. The other is that there are few ways like SN, which a person can provide some value and then obtain some bitcoin. When people earn in bitcoin, then they will spend in bitcoin.