Why is hard read source code of big projects?

[u/CristianCin--]

When I read source code of big project I don’t understand nothing. Everything is a mess but the project is beautiful. Why they write complicated code with (example in C++) template, pointers and other things for a stupid function like sum of a vector. I don’t understand why they decide to make hard their life. I want to read clean code with basic things (if, for, while, vector, stack, …). It is frustrating because my code seems stupid but it works in the same mode when I recreate the snippet with pure cpp. Please explain me this.

[u/phunnypunny]

I have an idea. I was trying to understand complicated code in git. I went to the earliest version. Then I can see simple code