>>58807496English thick pastel yellow border goes along well with the bright pastel monochrome body of the card, whose color is carefully chosen to make the pokemon's type immediately recognizable at a first glance. Golden border doesn't go well with pastel, and it looks more like a dark washed out yellow. Same for modern silver borders that just look like a colorless grey against the colorful body of the card.
For the same reason, yellow border on full arts looks like trash, without the colorful pastel body i'ts better to have a more neutral border, or you risk having a lone bright yellow that clashes with whatever color scheme the artwork is trying to convey.
