Amount of lithium in a single drone battery is minuscle. Quickly googled answer says that there's about 7% from weight lithium in a battery, so your average drone cell might have something like 10-20 grams of lithium in it (altough that 7% is for Li-Ion and drones tend to use LiFePo, so that number might be wrong). In a single electric car there's tens of kilograms of lithium inside. So a single car fire anywhere in the world "wastes" more lithium than hundreds and hundreds of drones in Ukraine.

Sure, it would be nice to recover that small amount too, but in practise we need a better material than lithium for our batteries. Also there's things like single-use vape-pens which use perfectly fine li-ion cell but it was manufactured without any means to charge it, a handful of those discarded on a nearest trash can (or more likely to the street next to it) is comparable to a single drone battery and people throw those away without concern every day.