Early parachutes of the era were too bulky & had a hard casing, & were fitted into the aircraft rather than worn by the pilot. They were used in observation balloons &, I think, zeppelins. The Germans used such chutes in 1918 fixed behind the cockpit.
There was also the belief that a parachute would lead to pilots being prone to abandonning their (expensive) aircraft too soon, or at the 1st sight of the enemy. Thereby totally disregarding the actual courage of the pilots who got into those aircraft, in the 1st place, & of the value of the training & life of a pilot, let alone of a skilled pilot.
(Note: Experience has led me to view these kinds of decisions as coming from the core personalities of the people making them, that they are judging others by what they would do. Which leads me to believe that many of the general staff of the period were cowards at heart.)
Because of the above, very little official research & development was conducted on improving parachute design. Post-WW1 a team of Americans designed the 1st practical parachute design, incorporating a soft casing, rip-cord & pilot chute in 1919 using ideas collected from pre-war designs dating back to 1906 & war-time experience with hard-shell parachutes.