And do lawyers typically incur considerable expenses during the course of their business? I guess I'm not really sure what outlays you are talking about.
Then, depending on your area of work, you've got issues like software to record and cite websites, continuing legal education requirements, etc.
Not the most expensive profession in terms of base costs, but not cheap either.
In addition, a 40 hour work week probably translates into something more along the lines of 20 billable hours given the inevitable variation in case load, personal time off for whatever, ongoing education, etc.
Basically, it's the same reason that any consultant-type job (which a small law practice effectively is) has to charge hourly rates that at first blush may seem pretty high just to translate into the equivalent of, say, a $100K salary at a typical corporate job.
*Some programmers have insurance but not to the extent that lawyers are required to have it.
Probably similar to your outlays.