I'm currently watching Wings again. It's just dawned on me, during this viewing, that WWI fighter planes (at least the ones I'm seeing used throughout this film) had fully open tops, that completely exposed the pilot on both sides, as well as across the front and back (though it looks like the wings structure went across the overhead area). Was the full front (I don't see any windshields), back, and sides exposure to help enable fast parachute escape if necessary, or was it perhaps more so to make the planes lighter, or perhaps to save money? Or maybe even for fullest range of visibility?

As you can see, the possibilities I've thought of simply are speculation on my part. But does anyone here, who's actually knowledgeable about WWI aerial warfare, know what the definite actual reason was for the fully open tops of the fighter planes of back then?