I'm curious though as to why governments haven't just outright banned cryptocurrencies?

Because they can't. How do they ban them? What would that look like?

An interesting side note here. El Salvador just made Bitcoin a national currency. They also said it won't be taxed, meaning capital gains won't be taxed, meaning that someone could get residency in El Salvador, and pay no tax on their millions in gains on the currency. This is huge. El Salvador could end up taking in billions of dollars just in economic activity as the result of this.

If countries try to ban it, they quickly find out they've shot themselves in the foot because Bitcoin is not bound by any country.