It's best not to take personally decisions made by mass market companies. American Express had the UK Centurion and Platinum cards priced incorrectly compared to other markets. It appears the decision has now been taken to raise the price, and they know full well that they will lose cardholders in the process. I daresay they even know how (approximately) how many.

The International Dollar/Euro Platinum cards cost $550/€550. The French card €590, German €250 initiation fee plus €500 per year, Netherlands €600 per year.

The USA cards appears to be a bargain at $450, but this includes only a single card. Adding three supplementary Platinum and five Gold cards brings the cost to $670.

None of this should influence your decision to keep the card, but the fee increase is not surprising.