Since the rookie pay scale was instituted before the 2013 NFL draft, it could take months to get your draft picks signed and into your building as agents were always waiting for the higher picks to fall before negotiating for their picks, no different than free agency where your elite guys are waiting for someone else to set the market so that they did not leave any money on the table.
Thankfully, teams and fans usually do not have to watch unnecessary drama to unfold; most rookies are signed within the first month of being drafted. The Falcons 2019 draft class is going to be counted on very early and the front office wants to get these guys in house as fast as possible.