People work because the kesubah obligates everyone to support their households. Choshen mishpat is a very complex area, and we need training classes- the equivalent of chosson classes. But living without parnassah is just not an option for most people. There are only so many wealthy in-laws and parents.
Furthermore, even if you don’t work, choshen mishpat questions come up all the time. You borrowed a car- are you allowed to fill up the gas tank? you lent your credit card- can you charge someone the interest if he didn’t pay you on time? Can you repay shekels with dollars and vice versa?
Finally, there are many non-entrepreneurial parnassas, usually available with a college degree, that don’t involve heavy choshen mishpat, eg accounting, programming, etc. The biggest kashye is on those who skip college because they’re too frum, and have to do some type of gesheft to support their family when money runs tight. It is in running a store that mos of these issue come up.