Sure, if you are doing it, killing fewer bystanders is preferable on the surface. But if individual assassinations are less likely to cause an international outcry since fewer people died that likely leads to more assassinations.
Wars being a terrible thing and all, one won't expect a speedy and fair trial on a battlefield.
It's mainly a local conflict with the superpowers backing different factions. Kind of like a proxy war during the cold war. A lot of countries backing opposing local factions while trying not to escalate.
A full blown declaration of war would give us WWIII in no time due to it being such a complex mess of alliances they're.
Rather than develop those missiles, what could be achieved by investing those millions into developing economies and relationships abroad?
It's the difference between sending an assassin and a suicide bomber.
The question by GP is more along the line of "what if instead of spending lots of money to kill fewer bystanders we spent that money to reduce the number of people that are so dangerous to us that we kill them".
Of course we know that won't happen because building weapons helps US companies and building hospitals and helping local people in foreign countries doesn't.
Or, after even the terrible decision of invading Iraq, if the US had been halfway competent / invested in post-invasion administration...
Like, would you rather drink a shoe leather smoothie or a shoe polish smoothie? Neither! Why are we drinking shoe related smoothies at all?!
Why do we need to assassinate anyone at all?
https://www.quotes.net/mquote/992742
"Paul Kersey: Nothing's too good for our friends!"