It works in GCC only and there are probably no guarantees that it will still work in the future. It also slows down compilation as compiler has to process much more files (unless you use it as intended — as a precompiled header, see below). There are several other downsides, they all sum up to "it's unacceptable in production code".

That people, as I think, use XCode (IDE) on MacOS. It IDE hasnt <bits/stdc++.h> header. P.S. it just my hypothesis and sorry for my ENG.

People who code in visual studio don't use it because it doesn't work there. Other reasons:

1. It slows down compilation time(doesn't affect execution time though)

2. On few OJs, Variable name y1 doesn't work with it. Example How to avoid it

It's hard to memorize?

A Noob like me sometimes write #include<bits\stdc++.h> And then it's hard to debug the error...

Ps: I don't do this now.. but it happened to me once.