A couple of reasons come to mind: 1. Your employer should be making more money off your work than they pay you. This means that they are worse off if they empl

A couple of reasons come to mind: 1. Your employer should be making more money off your work than they pay you. This means that they are worse off if they employ you less often. The reduced output will hurt them more than the reduced salary will help. 2. The business keeps going when you are gone. If you are a tech worker, part of your value is the ongoing development and maintenance of systems, or more generally your handling of some issues. This work has to be transferred while you are gone, which is disruptive. It’s like the switching cost of hiring and training, which your employer would prefer to avoid. Other commenters bring up consulting, where this can be clearly defined as not your job. 3. Although it’s a valuable benefit that could help attract talent, it could also select for less committed candidates. Asking for this in a negotiation suggests you don’t really want to be there.