Law firms know this, and get around it by delegating everything they possibly can to paralegals and junior staff while representing much more hands-on involvement by senior, experienced staff.
Sorta like software outsourcing, actually.
It’s billing fraud, and a critical part of the film version of “The Firm”.
Never hire a lawyer, then.
I hired an attorney once. I reviewed the invoices, the hours looked reasonable. Cue 4 months later with him saying he had forgotten to generate an invoice from a second record in his billing system - it had around 70% of additional hours. Between this and that he had been apparently ignoring one of my main concerns the whole time, only to wring his hands of responsibility when it ran aground, that relationship went south real fast.