Bitcoin legal tender = no capital gains tax. So if somebody is sending them bitcoin, they can sell it for USD and NOT need to pay capital gains tax. So a transaction from Western Union might cost $20 in fees, ends up costing $1 in transfer fee. You have effectively found away to send usd for $1 instead of $20.
In terms of holding bitcoin itself, if you zoom out in 4 years, charts always go up. So its more of a savings account. You have bitcoin at fixed supply, and you have currencies at infinite supply ... bitcoin will win over time, its just mathematics.