Oh? So you would be willing to leave your computer on permanently, and have it constantly bogged down to the point of being unusable pretty much indefinitely? Not to mention rendering is extremely taxing on your GPU, and even high end GPU's burn out much faster than they would under normal workloads.
Rendering is much more resource intensive than you might think. The last time I had a computer that was built specifically for rendering, I spent almost $5k USD, and after only about a year and a half, had to replace the GPU's in it.
Also, the software necessary to set up a service like you linked in your last post is anything but cheap. You know how everyone that builds computers hates cryptocurrency miners? Things like what you are suggesting is exactly how those guys turn a profit, and can afford to buy as many GPUs as they do.