For what it's worth, the somewhat hilarious reason justpaste.it is on the list is likely that it used to be a favourite of Islamic State terrorists a decade ago. https://www.politico.com/magazine/story/2014/08/islamic-stat...
Googling 'site:gov "justpaste.it"' also brings endless results of government documents mentioning the site in the context of terrorism.
I somewhat doubt US immigration authorities thwarted any would-be terrorists by asking for their justpaste.it username, but what do I know, perhaps this was an important breakthrough in the global war on terror.
You'd be surprised at the number of people who willingly give up their social media accounts, only for immigration officials to find comments in support of terror attacks in the Middle East.
It's pretty easy to think it's harmless if you live in a country where that viewpoint is not uncommon.
It can be an easy charge of “lying to the government on an official form” when they discover you have a user account somewhere that you didn’t disclose, even if they can’t get anything else to stick.