b) Finding evaders of sanctions seems like it should fall under a national security agency's purvue. We all take it for granted that the NSA could pinpoint our locations pretty easily, right? One thing that's particularly insane about the US government is how many departments have intelligence agencies. Obviously the ideal would be to have a small handful of well regulated intelligence agencies (emphasis on "well regulated", and you only have to look at the overreach by e.g. the CIA over the past 50 years to know that the US has had issues with that.)
c) The tax evasion contract looks at social media posts to find tax evaders. I wouldn't be particularly upset if the IRS had their own internal tech department doing this - if you're going to have a tax agency, you want it to be able to prevent cheating, otherwise the tax system falls apart. Finding people who have declared themselves to have beaten the system in a public forum is a cheap and easy way to go after cheaters.
There's a lot of pork in contracts that government agencies give out to private contractors, but this seems like a relatively low spend, and so it doesn't seem particularly bad that the IRS has decided that this is outside of their current expertise and given out a contract to chase it.