As a factual matter, you are quite wrong. Law firms rarely get reprimanded for over-billing, and in fact, the opposite can be true.
When a lawyer bills 2X more than a competitor, they can say that they just did a 2X better job, were more thorough, etc. Lawsuits are rarely repetitive, as the facts and legal principles applied vary widely, so it's very difficult to determine what's the correct amount of time to spend on something. Worse, firms that develop reputations for big bills, can even attract big bet-the-company cases where clients can justify paying top-dollar.
The economic principal behind this is that legal services are not a typical "commodity", so standard market principles are not as effective. If you can turn a legal service into a commodity (such as LegalZoom has some parts of the law), you can be much more effective.