I just purchased a Sylesti, and it said it was infertile. Is there any way to reverse this? :(

@Destinyflight,
Nope, there is no way to reverse infertilization. You can try contacting the seller to send the pet back to them for the price you bought it for.

My question is why would anyone want this anyways?

People who have made projects and sell them want it.
Whether it's a 6-vis project or a max-stat project, or any other kind of project, it's a lot of time and effort and cost on their part to undertake.
Making a pet infertile before the pet is sold means that other people cannot rebreed and sell offspring of their project- that they would quite likely have had to work on for months and months- effectively taking profit from them.

Here are my reasons why I'll buy infertile pets.

Generally max stat pets that are sold are infertile. I'll gladly buy an infertile max stat if I like the price. They're particularly nice for the battle leaderboards during the major fests so I'm happy to pick up multiple species of max stats over time as well.

If I like a project pet, I'll also buy it even if it's infertile. I don't do that much breeding myself and a lot of times I just like pets because they're pretty.

I'm not bothered by it. I don't need to breed everything I own.
And as others mentioned, people make their pets infertile to stop others from potentially profiting off of their hard long-term work.