> Why should visiting a page on your computer count as copying?

Because there's no physical mechanism for the information to be transmitted over a computer network other than by copying the bytes.

Note this is distinct from broadcast systems like analog television or radio. Packet switching networks only function by copying information and storing multiple copies around the internet, including in your computer's RAM (and disk, if cached).

So a legal definition that says "this kind of copying is copying but that other kind of copying isn't copying" makes no sense at all. Like many other legal definitions--it's all about what has been successfully snuck past a jury at one point or another in the past, without any heed for how things actually work.