The Netherland Palace has announced they are no longer sending out "thank you" replies to well-wishers for Birthdays, New Years, etc.
"The warm wishes received by the Royal Family on the occasion of birthdays and New Year's are always greatly appreciated. You indicate that you have not received any thank you cards since last December. It is indeed true that thank you cards are no longer sent for birthdays and New Year: thank the King and Queen for the wishes received via the Government Information Service and the official social media channels of the Royal House."
The Palace has not given any reason for this decision. But I expect it was likely a cost thing. The Netherland Royals have always limited what they send replies for. And when they did reply, they did a number of things to help cut costs, such as creating cards that can be re-used for a few years.
You can find some of my past replies from the Netherland Royals here.