Origin of the term:
The exact origin of the term Cumflation is unknown, it was however seen in Hentai as early as the 1990s.
Since then there was a massive rise in popularity of eastern culture and abstract pornography, so it has certainly become globalized in the 21st century, which is also when the term Cumflation itself was first used.
How it became popular?
Given the current trend around eastern culture and abstract pornography, there has been a massive rise in interest in things like Cumflation.
It is so present in modern day Hentai that the term also got its own entry in the Urban Dictionary in 2010.
Main online boards to help spread the word about Cumflation include Reddit and 4chan, as their communities seem to have the biggest interest in bizarre media of all sorts.