from the article "the second reason [they aren't just mining themselves] is far more practical: bitcoins, for all their current value, are still speculative. A

from the article "the second reason [they aren't just mining themselves] is far more practical: bitcoins, for all their current value, are still speculative. A large amount of US dollars is a large amount of US dollars no matter which way you cut it. It can be readily exchanged for goods and services. Bitcoins themselves don't necessarily hold value, and it's difficult to exchange them in large quantities for an equivalent amount of dollars. "