The purpose of textbook publishers these days is to convince educators that the new books add value, so they'll keep buying new books every year. Those images you're talking about aren't intended for the consumption of the child, they're intended for whoever makes purchasing decisions in the local school districts. Upper-management types are often delighted by bright, shiny objects.

It's not like the fundamentals of geometry change drastically every year. We're still pretty much studying Euclid and Pythagoras at that stage.