New charges being brought isn't that weird. They can bring fewer charges initially to more intensely pressure a plea deal. By doing that it makes the decision to "fight these charges" or "take the deal" less clear. Because by not taking the deal they might also bring additional charges. So it's take the deal, or maybe also deal with additional charges. This adds additional fear to not taking the plea deal because of the fear of the unknown. Also the initial charges might just be to get the arrest. For example, the Ross Ulbrict case had a lot of charges added after arrest. It also saves time with a magistrate if you don't have to go over every single charge you could bring against them just to make an arrest. Does the magistrate need to hear Ghislaine Maxwell's entire biography to make an arrest? If all of it is sorted, then you would be giving a biography if you had to bring every charge at once.