Is there a reason they’re on the left?
Yes. It’s that the ultimate button in this little micro “dialog” box (Window title bar) is the destructive action of closing the window, and Apple determined the ideal order of actions to be from left to right:
| Destructive || Neutral || Constructive |
Since the button on the far left closes the window, and is therefore the most destructive possible button in a window based GUI OS, it should be on the far left of the Window status bar that is its container when using these rules of lateral action distribution. This fundamental design choice informed the decision to put the close window button on the far left, the other two actions (minimise and maximise) are placed beside it because that’s now the area that is the “dialog box action area” of the Window Title Bar.
For a brief while we had the ideal of a super-maximise-to-a-new-screen-space on the top right, double tapping the middle section of the Window Title Bar to minimise and far left being the destructive close button with the minimise and maximise buttons next to it.
But then a (wrong headed) desire to put the download button and iOS sharing button in the top right of Safari seemed to override this ideal across all of Mac OS X, and we lost the normal and rightful maximise button in this little trio. It’s been replaced with the fullscreen, new space button. I’m pretty sure this little mess wouldn’t have happened under Steve Jobs’ watch.
In answer to your original question, yes everything about OS GUI design is intentional, and has reasoning behind both the intentions and the decided design. It’s just not always transparent, and sometimes not good intentions, like the desire to transplant the ideas of iOS sharing button placement to Mac OS X.