My theory of Finn backstory and why: Enter one of the hundreds of battles being waged at the climax of the Clone Wars. Mace Windu in full realization that there is a storm ahead, but doesn't know what when or how. Finds a one time lover on a distant planet. On this day, an extra dimension of meaning was added to his life for it would never be the same. A child is conceived. Understandings are exchanged, and Windu takes his place again at the center of galactic conflict. Referring back to Qui-Gon's words in TPM, "if Anakin had been born in the Republic we would have identified him early". Windu intended to go back when the time was right to oversee the future of his offspring. It was definitely in the cards for the Jedi master who by all accounts has been demonstrated time and again letting go of attachment and act in the benefit of the Jedi order and the republic. The timeline now is about half of the way through RoTS. Windu's romantic encounter comes to Courascant to find the Jedi master. But she does not go right away, she explores the vastness of a city of the likes she has never seen. [the rest of this paragraph isn't even necessary lol just for crowd effect]. She bumps baby bellies with Padme as they are both on their way to an impromptu pregnancy counseling session. Each says their parts. While they are each saying their piece, they leave out the force-sensitive complexity of their experiences. They part ways remembering one another but never seeing each other again. Reality sets in for the mystery lover after the order 66 events transpire. Knowing full well the probability of Mace Windu's survival she quietly leaves the planet. She further realizes that her son [ultrasound also done on Courascant], may also be in grave danger. She goes into a more discreet life. Fast-forward 28 years later and Windu's offspring is now fully grown at the conclusion of the battle of Endor. Has come to know he has special abilities as well. The force is very dormant however with this offspring of Mace Windu. Since an early age, abilities that his mother has discouraged him to ever use due to no reason in particular (however the mothers motivation of discouragement is due to the danger of the empire). The son of Windu never really uses the force or has visions. This son of Windu has a child as well, a little later in life at 35 years old This event places this new offspring, the grandson of Mace Windu, born 7 years after the battle of Endor. Deeply rooted in his genome now is a strong discouragement to really discover the powers of the force. This results in very dormant but not lost force ability, which would need some drastic rekindling. Although he may never use the force, the ability is present and actually does have the potential to be very strong indeed with the force. Finn is ultimately taken at an early age into the first order, but certain traits are not Lost and he finds his own way back to the light. Finn, grandson of Mace Windu, and a powerfully ally he is. Disconnected with abilities of the force, make him weak this does not.