Basically it's because it's THE bill signing desk. So usually there are a crowd of people around it.
Don't know if this was posted in that other thread you're talking about, but this tweet thread has pretty decent info.
Lol. Really want to know the steps in the decision making process to have Trump do a press briefing from that desk in that setup. Whoever planned all this must've been trolling.
Those Obama pictures.. Do they bring a box of pens like if they were some expensive cigars?