For much the same reason adult men between 18 and 60 are barred from leaving Ukraine at the moment: they're the primary pool of conscripts and recruits. When young men die it's never clear who was a non-combatant, while women are much less likely to be enemy fighters, and pre-teen children even less so.

If a drone strike kills five men, who knows whether they were enemy combatants? Your example is murky and vague, through no fault of the dead men. If it kills three kids under the age of 10 and two mothers, it's more obvious the casualties weren't combatants. If you're a journalist and you're looking for examples of clearly horrific drone strikes, you point to the one that killed people who were most obviously non-combatants.

I think you know this and you're asking a rhetorical question about the value of human life, but it's a question with a real answer. "Innocent adults" is a phrase less self-evident than "innocent women and children" because of the way militaries and insurgent groups recruit.