This probably differs a lot from region to region. I can only tell you how the playing card in Japan developped, because I wrote a paper on gambling in pre-Meiji Japan, based on "tobaku to suri no kenkyuu" (the study of gambling and pickpocketing), written in 1925 by Osatake Takeki.

The earliest playing cards in Japan originally were developped from variants on dice games, such as yoido, a simple gambling game with three dice. This can easily be proven by examining the transition forms of the game, which are still played in certain areas (in 1925, when Osatake wrote his book). The most common playcards in the Meiji-period were the hanakaruta or Flower cards, which are nowadays called hanafuda. The first form of these cards were the unsun-cards from the early Edo, most likely based on the card games from Portuguese merchants. This is the earliest mentioning of playing cards in Japan. These then evolved into tenshou-cards in the late 16th century. This game, in turn, was mixed with the age-old Heian period kaiawase ("match the seashells") played with cards that had seashell decoration. The seashell decoration was then changed to flower decorations, and they were put on the tenshou-cards, and so the flower cards were born.

Evolutions in cards and card games were mainly caused by two reasons: First of all, games were mixed all the time, and new games traders from foreign countries brought with them got popular really fast, but were often adopted into a more Japanese style. Regional difference in games are (as everywhere else, I assume) very large at times.

A second reason is more interesting though. Throughout the history of Japan, rulers have tried to ban gambling. The earliest bans date from 698 AC. Even though the punishments were very severe, this never stopped gamblers. They liked to evade these bans by continually making new games, which weren't banned yet. Making a new game gave gamblers some 'free' time in which their game was not yet technically on the banned list, and in which they could not be prosecuted. This ever-changing gambling scene has provided Japan with ample card game variants throughout the history.