The key figures to look at here are civilian casualties and relative populations. The German Empire had a population of 65 million, and suffered 750,000, whilst the Ottoman Empire had a population of 25 million, yet suffered 2.5 million civilian casualties. Most of these latter casualties are from the Armenian Genocide, which was instituted by the Ottomans so are almost 'self-inflicted'. Yes there was great casualties on the front lines of the Western front, but much more devastating movements were being made in the east, where trench warfare did not restrict movement to the same extent. Serbia was completely overwhelmed, and a complete evacuation ordered through Albania and Montengro, but this largely unsuccessful. Similarly once Russia had pulled out of the war, Romania was almost completely defeated and occupied.

Tl;dr Nations with much smaller populations were routed/ and occupied with a resultant increase in casualties. Ottoman Empire kills a large section of its own populace.

In addition to /u/rostafarii's note on the Armenian genocide, I would wonder how the figures in your question were calculated or what the source of them was. For the Ottomans I would be curious if that 14% figure is, for instance, just referring to the population of Anatolia, in which case it might also be including the expulsion of ethnic Greeks immediately after the war.