questions about link

[Chameleon]

My project uses many libraries like libjpeg, libpng and more.
With all of these libraries linked statically and with many .cpp files
of my project, a big binary executable is predictable.

I'm impressed when I was remove the code inside 'main(...)' and all of
the includes, but executable size doesn't change, at all.

There are many *.cpp files but in test.cpp which implements 'main' there
is only this code:
----test.cpp--------
int main(int argc, char **argv)
{
return 0;
}
--------------------

size for this executable is about 290KBs and inside binary I recognize
parts of zlib library. I use zlib library in other .cpp file than
test.cpp, but I don't call anything from this file and if I remove it,
all work ok and size decreases.
If I remove all files except test.cpp, it compiles fine and size is 10KBs.

So the question is why linker include useless binary objects to final
binary executable.

My compiler/linker is mingw-g++, if does matter.