If you browse the local files of Force Unleashed, you're going to find this little gremlin, depicted here in all its shame, circled in red.
This little saboteur is literally the only reason you can't start through Steam, unless your computer is haunted. If you select SWTFU.exe, your game will actually start! SWTFU Launcher.exe is the definition of a worthless middleman who makes things more complicated than things should be.

What happens here, is Steam tries to launch the game through the Launcher, but the Launcher fails at being a Launcher because the Launcher doesn't Launch the game. So, dear reader, how do we fix this?

Throw the launcher into the shadow realm. Rename SWTFU.exe to SWTFU Launcher.exe. It should look like this now
Now you should be able to launch the game through Steam.

Love this game, but this PC port sucks.