Iron Man 2 did not do the kind of box office that people were expecting.
Director Jon Favreau has Cowboys And Aliens to do
Robert Downey Jr has Sherlock Holmes 2 to do
Then Iron Man (Robert Downey Jr) is slated to star in The Avengers
Then Iron Man 3 will be made.
a) Its a few years before made/released
b) Iron Man 2 performed under expectations
c) possibility that if The Avengers is a hit that an Avengers sequel might take priority over an Iron Man sequel (= the future is not certain)
d) it is an expensive stock for smaller ports to hold long term (years), so their dumping causes price to go down, then smart investers dump or flip short causing the price to go down, which causes casual traders to dump which causes price to go down, then players see a pattern of it going down and short it causing the price to go down, then rich people who were going to hold it long term long see the profit loss and dump or flip it, etc.....
e) summer has started and ports are dumping development stocks so they can afford to invest in high priced summer openers