US investors are... lurking in the wings.
Even if this is true, this is the number one reason, Bitcoin will fail as a currency. Average people need to buy it and spend it. Investors just pumping the price up means nothing toward usefulness. It's a temporary and artificial valuation.
The infrastructure for that really isn't there just yet. There are plenty of projects on the way and we'll get there, but not yet. That's when it really takes off.