Developers do this. On the flip side, "product owners" or clients or "stakeholders" or whatever will, not infrequently, propose a little feature that is someone else's entire product.

I always try to point this out when it happens, and advise them to just pay for it, unless they want to create a competing product.

Bonus points for such requests when that feature/other-person's-product is probably more lucrative than the entire actual product they're trying to build. Which does happen, and never fails to be funny.