Why does this schematic have a "Do Not Mount" component? Why not just remove it from the BOM and drawings?
Many electronic designs have options, to accommodate different components (like a different antenna for example). Accommodating different components may require some component installed or removed. In any case the PCB has to have a proper placeholder for these optional components.

The PCB layout software therefore must have an information about these placeholders. In modern CAD tools the schematic database is usually integrated with layout tool and its database, and exhaustive check for connectivity is usually conducted, to avoid costly board re-spins. If one wants to remove a component from drawing, it will cause mismatch in databases, and will generate lots of errors. As result, manufacturing/production engineers prefer to keep their databases consistent across all tolls, which is the reason why the DNP (or DNM) components remain in schematics.