Let me say it in a different way...
Again, HEDT platforms/CPUs do not have an iGPU, you NEED a GPU for that platform. None of the boards have video outputs! Sure, you can buy a lower end platform that has video outputs on the mobo and an iGPU in the chip, but, what if you need more cores and the power that the HEDT platform gives you but don't game? A card like this would fit in perfectly.
Also, people buy boards that don't have the outputs on the mobo and either need to buy a motherboard, or a GPU. Which of those is cheaper and easier to change out?
There are plenty of reasons for these cards to exist... I would imagine one of them is to prey on the ignorant, but, there are good reasons why they exist too!