Why are they trying to make him an action star?

Liam Neeson always had action credentials along with dramatic ones, he's in a similar vain to Harrison Ford, and his career followed a similar path to his in that Ford became a big action guy the 90s after doing more dramatic stuff in the mid to late 80s, so Liam was basically Ford's successor in the 00s.

Neeson was the best thing about The Phantom Menace, and the best acting performance of the whole prequel trilogy, and he played a Jedi Knight, so I wasn't surprised to see him go on to become an action star.

Noone is trying to make him an action star. He takes those projects because they do not require the type of acting commitment that movies like "Schindler's List" need and they are an easy paycheck for him.
Now you are asking why he does the easy stuff instead of the hard stuff?
The death of his wife Natasha Richardson was a devastating blow to him and I read that he almost gave up acting after it. Now, he wants to relax in films.