This might be more of a blogosphere-era thing I guess. Even when most people blogging did it for pleasure rather than work, it was always considered polite to “hat tip” (h/t) the source of a given link, if you happened to find it on someone else’s site.
I imagine it’s because it’s the simplest, most common type of ball that you commonly see described as such. Like, baseballs and basketballs and soccer balls and beach balls exist, but out of context they’re typically called that rather than just “a ball”. So, a simple round ball. Giving it a pattern requires some extra thought, and of the solid colors red seems like the most common (think dodgeballs).