No, it's a feature not a bug. If you don't index things to inflation you can eventually cover average and middle-class amounts of money under the law - you just have to be patient.
More likely the number 10000 is now entrenched in so many varied locations in the last 50 years that it would be a monumental undertaking to try and adjust it successfully.
If the rule is > $100k, can't businesses just continue reporting everything > $10k until they get around to updating their systems?