Because they won't. Most will adapt. It will be a very small amount of people that will stop playing, probably because the FSS does not dictate to them whether they enjoy the game or not. They can get over it. What's done is done. Is it worth the effort and potential issues of adding it back in just for the very few the stop playing.Why drive away even 1-2% of your playerbase unnecessarily?
The beige plague happened due to an unforsee issue of optimasation of planet surfaces so they could run better as FPS would tank on every system.The beige plague was a bug, and was eventually fixed by an overall rework to planet surfaces.
It did get fixed and the reason why it took so long, you have already said. They had to do a complete rework of the shaders.It didn't get fixed because of players complaining.
I think it was the forums on the whole. Nobody want to fly around in space looking at bland planets. But okay then lets say around 90% of explorers and about 50-60% of the rest of the forums. It is still a significant amount of people of the forum users.Also, while it might be 80-90% of explorers who complained about it, it certainly wasn't anywhere near that percentage of the forum as a whole.