Why would you make a pet infertile and then sell it? I'm genuinely curious. What is the reasoning behind it?

I'm mostly on here for the breeding function, and I'm still figuring out the site and how to read certain functions, so imagine my surprise when I purchased a pet that is unable to breed, and the effect seems irreversible. If you're curious, I'm selling it for the same amount I bought it for, hoping to make back the gold

Generally, people make pets infertile in order to maintain the value of a project they worked hard on and put a lot of gold / diamonds into.

For example, if someone were to do a maximum stat project, it would probably cost them quite a bit (Prismatic Philters are currently 48 diamonds each and you'd need approximately 32 of them to get to project completion and that doesn't include any gender swappers you may need and assumes you buy all Philters when they're on sale).
They're not going to want to sell the pets when they're fertile as people could then use that pet to breed pets that had stats anywhere between maximum stats and the stats of that pet's breeding partner (if the breeding partner had max stats as well then any offspring would have max stats).
Selling the pets fertile would corrode their investment in all those diamonds, the time their project took, etc.

Same goes for projects for particular designs / colours / traits - essences and dyes don't come cheap so some people look to preserve their investments.

Its possible to check if pets are fertile / infertile before you buy them.
You just need to take a quick look at their profile to see if you can see this image:

There are breeders who put in a lot of time and effort to get a pet a certain way, wether it be multi-visual, specific colors, specific traits or even stats, many of which start off with low GP pets or generated pets. The point to making a pet infertile is to protect the investment of the time and resources they put in to the project so that other breeders can't take their hard work and use it as a get rich quick gimmick.

I personally just bought an infertility philter kit, but it's mostly to use on stat bred pets for new users who are having a tough time with battling, specifically because I stat pets with prismatic philters.

Obviously not everyone agrees with the practice of making pets infertile, but I do see the need for it in certain cases. Please remember to check to see if pets are infertile before you buy them if you don't want infertile pets.

Interesting. I can understand why some would want to protect their investments. I imagined it might be way to protect their art so it couldn't be duplicated. Thank you for your insights