Probably because paying that tax is just extra paper work that doesn't have to be done by the employee. So let accounting of your employer figure it out. Incom

Probably because paying that tax is just extra paper work that doesn't have to be done by the employee. So let accounting of your employer figure it out. Income tax on the other hand is something the employee will have to figure out himself, because he may have other income streams. This keeps the work where there is expertise as much as possible.