Q: Is it hard to start a project like this?
A: Depends on how you start the project. Do research, look into the type of point and click game you want to make. Think of different stories, characters, do some doodles on some paper for rough scenes and scan it into UE4 to see what you can do with it. Any project requires a decent amount of prep work ranging from research to planning to development to publishing.
Q: Why hasn’t anyone done 2D point and click games in UE4 yet?
A: They kinda have but the sad problem with 2D point and click games is they are dying (Adventures games are not dead ← see if you get that reference). On top of that there are always some basic game engines out there which allow you to create point and click games.
If you have any more questions you would like the answers to, please feel free to ask. Like I said though all of this is just my opinion and from my own knowledge + experience of using the engine and from my job.