Bloody April was so named because of the high proportion of casualties sustained - and the unrpecednted rate of losses - compared to the number of aircraft/pilots available. Perhaps also because of an apparent or perceived imbalance between the British and German losses.
The numbers of aircraft and aircrew lost in 1916-late 1917 were a tiny fraction of those operational in early to mid 1918. In mid 1918 the numbers of aircraft and aircrew dwarfed those of mid 1917. By the end of 1918 the numbers were colossal. In 1918 some aerial combats were reported to number dozens and scores of aircraft on each sides - casualties are inevtiably higher when more people are involved!
Aerial combat was only one way of many to sustain casualties - ground attack operations increased substantially in 1918, as did long-range bombing operations, naval cooperation, home defence etc. These kinds of oeprations have a different probability of casualties being sustained than combat patrols or over-the-lines army cooperation.
Likewise, aircraft and aircrew were prone to catastrophic mechanical failures. "Pilot error" losses and other non-combat losses were substantial at all times. I have no data but I suspect that early war casualties may have had a much higher proportion of non-combat losses than occurred later in the war. Anybody have any facts to support or reject this view?
Another factor - in the earlier period of 1916 to mid-18917 the proportion of fighting/Jasta units to army cooperation/"working" units was low. I estimate (and am open to correction) that in 1916 far less than a quarter of units were deliberately intended to gain what is now called air supremacy by engaging enemy aircraft. By the end of the war I am sure it it was well over 50% for front-line units on active the Western Front. In the early days a small number of fighting aircraft going out deliberately to bring down opponents could have a disproportionately high effect (viz the so-called "Fokker scourage" featured a tiny number of aircraft compared to later air fleets). Larger groups like "Richthofen's Circus" could have a disproportionate lcoal effect by bringing temporary air superiority to whichever sector it was posted. The allocation of the RNAS scouts units to the Western Front also had a powerful localised effect.
By the last few months of the war ever larger fleets of Allied aircraft were able to sweep the skies to achieve air superiority and inflict shattering losses. The more fighter planes the more losses, it's a mathematical truism.