Playing devil's advocate, since 631 instances in the first half of the year is a "minuscule fraction" of flights and passengers, the 3 hour rule seems to be a good compromise. It only affects the "minuscule fraction" of flights but puts a burden on airlines to not hole up pax for hours on end.

And yes, the $27K/passenger fine is excessive, but as was said, it is meant as punitive so airlines have a reason to avoid it. Most DOT fines that are imposed on airlines are a joke - very small amounts to begin with and at least half of the fine is waived if the airline doesn't have a similar incident within X months.