In the days before credit cards (yes, there really were such days!), when the only type of 'plastic card' available was American Express (where you had to pay the balance off in full at the end of each month) a 'gold card holder' was someone extra special. (i.e. very, very wealthy!). Such a card could be used to buy a fleet of Lamborghinis and Ferraris, together with a couple of massive yachts and loads of mega-expensive jewellery, all on the same day without there being the slightest question mark over the cardholder's ability to pay his bill at the end of the month.
With the advent of credit cards, banks continued to keep 'gold cards' for their most favoured customers for a while but then used the idea of being able to get hold of a 'gold card' as a marketing tool to draw in the gullible.
Once everyone had got used to the idea that a 'gold card' was no longer particularly special, they repeated the ploy but using the term 'platinum card' instead. Once again, though, we've reached the stage where almost anyone can have a platinum card, so again the name is really meaningless. A 'platinum' Barclaycard is now the ordinary one which most people get. Only people with a poor credit history, who're seeking to build up their credit score, are given an 'initial' (i.e. 'non-platinum' card).
Having gone through 'gold' and 'platinum' , it will be interesting to see what the banks come up with next, which is even more valuable than platinum. An 'inkjet printer ink' card, perhaps?
;-)