1- Doctors often work very long hours. (Why not "work for..." ?)
2- He worked the clubs long before TV made him famous. (Why not "work in/for the clubs..." ?)
3- I am working a drug case. (He is a detective.) (Why not "work on a drugs case" ?)
4- They are thieves working a very long con. (A long con:A long con or big con is a scam that unfolds over several days or weeks and involves a team of swindlers, as well as props, sets, extras, costumes, and scripted lines.) (Why not "work on/for a very long con" ?)
Why we don't use preposition in these sentences above?