Also, the pellets have a steady supply of protien in them that if turtles get too much of it will lead to overgrowth and a number of health issues later. So after the first year of growth, they should be averaging about an inch a year after that. Cutting back the pellets to every other day would be good for this.
And as turtles age they do become more herbivorous, eating more veggies/plant matter than when they were younger.
Does this make any sense to you? I have never really thought about about the specific reasons of cutting them back, but these are the most logical reasons to me why it would be done. I'm sure someone could have said it much better than me though.
Here's a quote that I found on a web-site:
Young sliders tend to be more carnivorous than adults; eating about 70% animal matter and 30% plant matter. Adults eat 90% plant matter and 10% animal matter
