Why do all new decks of cards have the first two suits in sequence followed by the second two suits reversed?
Sorry for the late reply.
Traditionally, it wasn't always like this. As a kid, I recall new deck order as having Ace through King for all suits, in the order of spades, hearts, clubs, diamonds. Now, it's spades, diamonds, clubs, hearts, with the first two sorted Ace through King, the last two sorted King through Ace.
The reason for the change was that through mathematical analysis, likely at the behest of casinos, it was learned that a deck's order doesn't get sufficiently randomized enough after shuffling when the suits are all four in the same order, new out of the box, resulting in detectable patterns - sometimes even when utilizing a deck wash to try to randomize the cards! Ever since, many manufacturers - including the largest one in the US, the United States Playing Card Company (USPC), started using what you now know as new deck order.