In 2009, out of 503 films released all together, only a small amount of 31 films were of the thriller genre.
Also, suspense/ thriller films only take up 4% of the year's box office. This is due to the age restrictions.
Here are some covers of a few thriller movies. Look at the age restriction.
As you can see there is a general age restriction in thriller films. This ultimately narrows the audience for thriller films and jeopardises the success of their film and percentage of views.
Also, it is a known fact that it is teenagers who visit the cinema most, this could influence sales to either watch it or alternatively deprive them from it due to the age restriction.
By looking at the 'genre by gender' diagram we can see that suspense is slightly more to the female preference than the males. However, there are aspects in thrillers such as Crime, Action and Sci Fi which judging by the diagram tends to appeal to males more.
Action, animation and comedy account for 52% of Box Office in the UK in 2009. I think this is because they generally have a wider target audience than thriller movies. Action movies are said to appeal to males more than females, and while this is true, it's highly rated by males judging by the 'genre for gender' diagram so it will get quite a lot of views. However unlike action- animation and comedy are quite diverse with their target audience and can appeal to almost any gender and any age- which explains the 52% take on the UK Box Office.