Its competitive value in battles and its status as a fan-favorite legendary Pokmon make it one of the most desired cards from the SV10 set
If you look at artifacts from the early days of Magic (like Alpha/Beta/Unlimited ), on noncreature artifacts, you'll see that there's extra words on the type line: "mono", "poly", and "continuous"
Expedition Reverse Foil ...but at least it was pretty and nice to look at
So despite this being just a Basic Energy card, not known for holding their value, perhaps the gold variants scarcity, along with the fact that its now a defunct Energy type, has contributed to it holding a pretty high value
More on this later about whitening but take into account that graders are trained to keep the customer happy
I have mixed feelings when it comes to things like Secret Lair and Magic using other IPs, but I remind folks that Magic is created by human beings with feelings