Why couldn't they?
Because they have already done that and it failed. The USD was pegged to gold up until 1971, at which time the Nixon administration arbitrarily decided to cease USD convertibility into gold. The USD has lost 83% of its value since that time. This is the entire problem bitcoin solves.
That doesn't make any sense. You're saying the USD was pegged to gold until 1971. That's true. So that means that they
can in fact peg it to gold. Just that it will fail eventually. I wasn't saying it won't fail, it will, but it will take decades to fail. Maybe even 100+ years just like how the USD is still around.
So again, why can't they?