Question: Without mouse support enabled (my default), you can drag your mouse over text and do standard "copy/paste" with right click, which enables you to paste the test anywhere on your operating system or browser. However, if i make the text with M-A, i have to copy the text with M-Shift-6 (M-^), why did they design nano like this?

Answer: 
The classic X11 copy/paste (mark text with left mouse button, paste with middle button) is not done by `nano` but by the terminal emulator itself.

(If you use PuTTY as your terminal emulator, paste is usually the right mouse button instead, as the existence of the middle mouse button is not guaranteed in mice designed for Windows.)

As far as `nano` knows, "you" are just re-typing the marked text very rapidly.
The terminal emulator is actually re-transmitting the characters on the marked text block back to the TTY standard input just as if the user had typed them.

This text copy function is very primitive, but since it is implemented by the terminal emulator (i.e. `xterm`, GNOME Terminal, or PuTTY), it is available for all text-based programs without any special support required.

If you enable `nano`'s mouse support, it tells the terminal emulator to override this default copy/paste functionality with a more advanced terminal-emulator-based mouse support. Then the terminal emulator will just send `nano` special codes to describe any mouse events within the terminal window, and `nano` will be able to decide what to do about them on its own.
Nano has its own clipboard, while your GUI has a different clipboard. Nano isn't a GUI program; so, that's probably why it doesn't use the GUI's clipboard (it's designed to run on systems that don't even have GUIs, and shells don't always supply a clipboard; so, it needs its own).

You could make Nano's copy and paste use the GUI's clipboard, though, believe it or not.

In the meantime, however, terminal emulators often have shortcuts to use the GUI's clipboard on the command-line (for instance, on gnome-terminal, on my system, pressing ctrl+shift+c will copy to it, and pressing ctrl+shift+v will paste from it). However, unless you configure Nano's own copy/paste to do it, selecting text with the keyboard won't allow you to copy that selected text with the GUI's clipboard.

To my knowledge, Nano's clipboard isn't interoperable with clipboards of other command-line apps, either.