Because they were missing important parts of the spectrum. Putting a gel(filter) in front of them to filter out another part of the spectrum doesn’t add back in what’s missing to begin with(and now you’re working with even less color[spectrum]). The green push is one of the biggest things I hated about early and cheap LED’s. Even today, some expensive ones still aren’t great. I have two Nila’s, which are arguably good quality lights, but they still have to have at least an 1/8 or 1/4 minus green, especially if working with other sources.
I have a lot of LED’s that I really like, now, and I have more money tied up in LED’s than I ever have in lighting before, but they still can’t make skin look as nice as good ‘ole tungsten. If nothing else matters except how the person ultimately looks on-camera, one of my couple hundred dollar Arri 750 openface tungsten lights in a 2’x3’ Chimera is better than one of my multi-thousand dollar Gemini’s in the 2’x3’ softbox.
Yeah after a while one digs deeper and finds that the better light sources have a continuous color spectrum (closer to a black-body emitter) vs. major spikes and dips:
This would have been very helpful back when I first started buying LED lights! https://indiecinemaacademy.com/complete-led-color-database-cri-tlci-cqs-tm30-15/