A merchant, i.e. someone who is selling, must buy from their suppliers.

If the merchant takes BTC and their supplier does NOT, then thy must convert to another currency, one which their supplier will accept.

As more business and people take BTC as payment, a self-reinforcing process begins, in which BTC will become more accepted, as it is more accepted.

See how that works. We call it positive feedback.

This is why you see what you seen now.

K