Trilux do it! The Lumega! I think Philips should do it and bring back the SGS!

Mainly because LED and HID lanterns have different requirements, an LED only needs to be able to fit a rectangular driver, terminal block, photocell and a surge protector in the gear chamber, as well as a flat LED pannel, with a heatsink on top. This is all very thin, and uses the minimum amount of material for the best performance, whereas a HID lantern body would have lots of wasted space and wouldn't get proper heatskinking while also using more materials, creating a more costly and less reliable lantern.

With that said, Philips did do an LED version of the Selenium and currently make a modified LED version of the Iridium.

Why don't they do the Selenium any more?

Presumably wasn't selling well and was costly to make. As LED technology advanced and they made newer designs, there was no reason to continue the selenium.

Thats just my guess though.