10% Service charge

In so many restaurants, quite every, the 10% service charge is not included in the meal/drink price. As a great mathematician of the 21th, I could argue, that this charge could easily be included in the prices resulting in better overview, easier understanding, etc. I just don't get it, why they exclude this percentual price. the same with VAT by the way. I would even suggest to make this as a law. Any contras/comments/confirmations?