If Russia is willing to spend cash like that, then of course they're willing to run massive bot farms to pollute any forums they can. I'd be shocked if the US was not doing the same in any way they can. You have to ask why Trump killed Radio Free America as well when it was clearly not an big expense.
Not sure how this relates to the subject in a direct way. Radio Free America was a outlet explicitly created and utilized to spread US propaganda, but kinda sorta barely disguised as a journalistic enterprise (not really, if you were listening to RFA you knew what you were listening to.) Shutting it down seems to be a counterpoint to all of the covert participation of US intelligence on the web which has done nothing but escalate.
The obvious answer to that question is "because he's a Russian asset". But that doesn't mean the obvious answer is also the correct one.
IMHO, we're seeing another and much more concerning trend at play here... the utter and complete rejection of anything but violence by the far-right. Diplomacy? Development aid? Cultural exchange? All sorts of soft power have been under attack for decades now, and not just by the far-right but (especially when it comes to development aid) also by mainstream centrist parties across the Western world. And it's always pseudo-masculine / "strongman" BS backing the sentiment - Bernd Höcke, German AfD mastermind, comes to my mind with "we have to rediscover our masculinity" [1], so do Hungary's Viktor Orban and his denouncement of LGBT or Trump's entire Œuvre.
I'm not saying that violence or at least being prepared, ready and willing to use it is automatically bad. Far from it. But all the various forms of "soft power"? They have a lot of value, value that the far-right is all too willing to just burn for entertainment.
[1] https://blogs.taz.de/zeitlupe/2019/03/24/die-auferstehung-de...
No matter where you look, the far-right kills and maims substantially much more people than the far-left does.
If AI is being used in these areas it is less as an attempt to manipulate as it is to just create noise and engender distrust in what they hear.