Because it's a window, not fullscreen. On windblows you have the task bar to consider. On the mac you cannot have windows that overlap the title bar at the top of the screen. I don't think any apps can open that cover the title bar on the mac, be they BlitzMax or otherwise. You could have a full-screen-size window with maybe no border or something (if maxgui allows such a thing), but you'll still get the title bar. That's really down to the o/s not Max.
You also should consider that if you use window mode it will be slower because it has to physically copy the pixels from the backbuffer to the visible buffer in a blit operation, whereas in fullscreen mode it becomes possible for the hardware to do a hardware flip, whereby it just changes the address of the memory it wants to look at rather than moving any data. So window mode is slower. If your window covers the whole screen you might as well go with fullscreen mode.
The only benefit I can see is that on some systems like my ibook, where the OpenGL implementation does not support full-screen contexts (window only), it would then be nice to be able to have a window that fills the whole screen, without a title and overlapping the title bar. But alas. These things are o/s constrained I think.
You also should consider that if you use window mode it will be slower because it has to physically copy the pixels from the backbuffer to the visible buffer in a blit operation, whereas in fullscreen mode it becomes possible for the hardware to do a hardware flip, whereby it just changes the address of the memory it wants to look at rather than moving any data. So window mode is slower. If your window covers the whole screen you might as well go with fullscreen mode.
The only benefit I can see is that on some systems like my ibook, where the OpenGL implementation does not support full-screen contexts (window only), it would then be nice to be able to have a window that fills the whole screen, without a title and overlapping the title bar. But alas. These things are o/s constrained I think.