Gresham's Law poses a decision between 2 alternatives: 1) Silver coin with 100% Silver, and, 2) 'Silver' coin with 80% silver. Only 1 factor is involved in this decision, the % Silver content, so the choice is easy: choose the 100% Silver coin.

Bitcoin vs Fiat: Decision problem involves ~10,000 factors, both known and unknown, so people are hesitant about making a decision with so may factors involved.

Most people are "Dollar invested" through job earnings, Social Security, 401k, etc. Hedging with Bitcoin makes sense, in case the default, heavy "Dollar investments" lose value.