Why there are no open source games made with a popular engine?

I was looking for a project that I could contribute to, but I didn’t find a single open source game with any of the popular engines (unity, ue4, cryengine), why is that?

Is it license related?

None of the engines are open source so you are not allowed to share the source. For example, UE4 allows you access to the source code but only for development of your own games and you cannot share any of it outside of the compiled game.

The easiest option would be to make an example game and put it on the market place. There’s a few Unity projects like that as well.

A more complicated option would be to come up with some solution where someone could download the specific version of UE4 you used, and the developer have an automated process (an .exe?) that adds and appends the changes the developer made to the engine files, as well as contains the project files.

you can contribute to Unreal Tournament 4. It’s free and open-source

There is a couple of open source unreal 4 projects, though:

Tom Looman’s survival game is the closest to the game you can find, I think.

I’m not sure about that, they either have the approval from Epic or they aren’t a complete game.

It would be cool to have a remake of an old game, for example one of the old final fantasy game. That way in time they could improve rather than be left to die.
But I can’t figure it out if it can be done with Unreal or not.

I’m sure that I cannot release Epic source codes but it shouldn’t really be required in the first place, I want to share my assets and scripts, but I don’t know if I’m allowed to do that.

You can share any code or content that you create yourself, so if you want people to be able to edit your game, you can provide your project files and then they would just have to make an Epic account and download the appropriate UE4 editor.

Sorry to necro this, but does that mean that if you used a vanilla version of the engine, and just extended from it, you could open-source your extended code/assets, and epic would be ok with it? Because people would still need to download the engine/ sign the EULA for it to run?

Right, any code you write or assets you create are yours and you can share them as you please, but you can not share/redistribute any of the engine.