Government contracts are extremely lucrative and usually long term, most companies would accept this work.
from what the article here says (i don't know more about it than that), it's not clear to me that google is doing more than selling their cloud video analysis products to a customer for experimental use on unclassified data. and this kind of sale necessarily comes with offers of (paid) support and consulting services because customers need help. one might object to this customer, certainly - but if so, one might ask, to which customers is google's cloud business not supposed to sell services on this basis? google has never pretended that it didn't sell its products to the defense and intelligence agencies at all; keyhole (google earth) was for many years a major product in the GEOINT sector [0].
if one's objection is to folks working on anything relating to a military or intelligence problem, well, a very large fraction of US senior faculty have taken funding from defense agencies to work on unclassified versions of applications: tracking, image/video/text analysis challenges, etc. etc. etc.
Rough guess, it might be that we're less than 10 years removed from "Do no evil" being part of Google's motto. While completely unsurprising, it's still disappointing to see how money wins versus ethics. But hey, shareholder value!
Edit: I was slowed down for posting too fast so I'm adding my reply to IntronExon here:
It's an interesting hypothetical but I'd argue its appeal is mostly in its simplicity with little evidence to support the claim. The instances you've cited happened either due to a failure of accurate intelligence or because intelligence indicated the structure was being used by enemy combatants. It's very possible to arrive at the conclusion that any unnecessary casualties which occurred happened as a result of poor military intelligence which better reconnaissance drones could help with. It's equally possible that someone working on this kind of technology could see its field use against groups like ISIS as evidence that weaponized drones are a useful tool in fighting terrorist organizations. Obviously neither of these will be true in every instance, but without strong evidence it's hard to believe that the matter is as simple as "some people are just unemphatic".