What are you talking about? Manga sales in Japan have been steady at around 6 billion dollars over the past 20 years. Comic book sales in the US have reached 400 million dollars recently, Europe is also very large (probably larger than the US). Brazil also has a prosperous comic book market.
Sales may be awesome overseas, but when comics first came out there was such a ridiculous demand in the 40's and especially the 50's they were churning them out like cookies. Oh those old golden age stories were so awful
. Most of those stories were written by people that worked in the office. No real true creative storytelling occured until Marvel Comics came out.
The amount of money comic books generates is a whooooole lot different than how many comic books are sold. More people read comic books back in the 1940's-1980's. In the 90's Marvel went public and everything changed. To answer to their shareholders Marvel was constantly doing some crossover gimmick, foil covers, and just endless marketing strategies to excuse hiking up the price.
The comic book shop became a thing of the past. Marvel, in another strategy to show shareholders more money, wouldnt use Diamond to distribute their comics anymore, and would only sell direct to stores. The storeowners cost to fill their shelves instantly doubled. As time wore on the small shops shut down. The cost of a normal comic book todays around 2 dollars, and the Marvel universe is more carefully crafted by moviemakers then Marvel themselves. Except for X-Men 3 and the Wolverine movies of course.
The absolute best time to be a comic book fan was in the 1980's. That was camelot. More units were sold, and their were true loyal fans of that comic book that came out each month, not just the charater. X-Men were hot, Daredevil written and drawn by Frank Miller, heck even independent comics were surging with Teenage Mutant Ninja Turtles, First Comics, Dark Horse, etc... The stories and artwork were at their best.
They just make more money now, but this isnt the golden time.