For a lawyer, if they put in 100 hours to come up with a 2-page letter, they charge for those 100 hours. The next time a client comes to them with a similar problem, they charge for 100 hours.
Software developers charge for time actually spent working on a particular project. If they reuse code, they don't (typically) charge anything. If developers were to charge for the number of hours spent writing that code they're reusing, they'd be more like lawyers.
For a lawyer, if they put in 100 hours to come up with a 2-page letter, they charge for those 100 hours. The next time a client comes to them with a similar problem, they charge for 100 hours.
Software developers charge for time actually spent working on a particular project. If they reuse code, they don't (typically) charge anything. If developers were to charge for the number of hours spent writing that code they're reusing, they'd be more like lawyers.