I don't get the point of making Sylestis infertile. Would someone be so kind as to shed some sort of light on the matter?

If you've ever had a project and sell pets fertile, you'd know you end up getting people breeding your offspring to sell at a cheaper price. It's mainly to stop people from selling your offspring or your offspring's offspring at a cheap price and making yours go out of value since you can buy them cheaper.

For example, my violet guardian pair. Someone bred two offspring with their own pair and are now selling offspring of a slightly changed colours but same traits for cheaper, making no one buy my original ones.

Max stat pets are another project pet that benefit from people being able to make offspring infertile. My vul max stat project took 34 prismatic philters, 9 gender swaps , and more pies than I cared to count. That is a huge investment. If someone could simply buy a fertile max stat they could use it to bump up the stats of any pets of that species and bypass all of the costs. If I couldn't make offspring infertile, I'd just do the projects for myself and not sell any offspring.