Also, it adds up (no pun intended). You're right that add() vs. + for a simple case when you only do it a few times is no big deal. But it is a bigger deal when you do it a lot, and the arithmetic can be a little more complicated.

We could by analogy apply this argument to adding integers and floats together. It's more convenient to use the + operator for that, but someone could argue that an add() function is just a minor inconvenience, so why bother overloading the + operator?

That is until you have to use it hundreds of times.

It's not just arithmetic, it's also being able to use comparison operators to filter, which is really convenient. What languages like R do at the syntactic level is make the programming language closer to math, where you can do things like add vectors or multiply matrices using simple operators.