First, it allows businesses to advertise lower prices than consumers will need to bear. It's similar to the American habit of adding sales tax at the point of sale instead of including it in the posted price that way. And because, as a species, we're prone to anchoring effects that causes us to systematically underestimate what the final total will be. That's pretty good for proprietors of service sector businesses, but probably slightly bad for the economy as a whole.
Second, it allows those proprietors to price discriminate a little bit (because price sensitive customers will sometimes buy the service but not tip) while pushing the downside risk off onto their employees.
And that's not even touching the way tips allow customers to de facto discriminate against staff (conventionally attractive people get more tips), or staff against customers ("black people don't tip"), in ways that would be anywhere from suspicious to downright scandalous if they were implemented more formally.
This doesn't mean you shouldn't tip well. You absolutely should, as service workers depend on tips to be fairly compensated for their labor. But tips are a bad idea and there's plenty of reasons beyond social awkwardness to wish they would go away.