Why such a large Unity/UE4 project exe file?

Question

Unity

It is interesting to learn about how developers reduce the size of .exe through game engines such as Unity and UE4, add their resource folders to the game build and why this is done.

For example, if I make a game, then the folder will contain some standard engine resources and an executable file ~ 30mb in size.

If you open a folder with a game from some other developers, you can see there some resources that you can even change, which leads to a change in something in the game, and the executable file is only ~ 10mb in size.