1 hour ago, Tramp Graphics said:The reasoning was simple, really. It allowed them to provide more detail about each given line's focus without skimping on "world-building" detail or game mechanic rules. If they had crammed all of it into a single core book, they would have had to cut out a lot of key "in universe world-building" information needed for role-playing the different types of characters in the setting in order to accommodate the game mechanics. As such, it would be heavily stripped down. By splitting it up into three lines, they could provide all of the rules needed for play without sacrificing any world-building and thematic focus, thus providing a much more complete game for each theme.
It also allowed them to slowly roll out the force so as to not imbalance the game. It also allowed to tailor careers to the three different genres. When they asked people what was star wars to them they got 3 answers.