It's a more recent occurrence. They are doing this so they aren't identified. It's why they sent HSI and Secret Service to the raid in California after a local had identified a bunch of ICE agents. They know being identified publicly will come back on them.
I worked at ICE HQ in 2013/2014 doing FOIA and Privacy Act releases. While a lot of the agents were garbage then also, they absolutly didn't wear neck gaiters and balaclavas to hide their identies.