There was nowhere for a new villain to come from.
Of course there is. In fact, the destruction of the Empire and the time between ROTJ and TFA provide a perfect opportunity and backstory for something of that nature to occur. I would even say that having an old villain back, and someone as high-level as Palpatine, makes less sense with the destruction of the Empire. And a trilogy is a great way to build up and grow the backstory, both in setting and characters. It then provides the new heroes some threat of their own to deal with (something I felt was lacking), giving them a sense of urgency, to fight it alongside the older heroes. The key is in creating. Disney had everything at their disposal, and every opportunity to turn it into gold.
Here's a quick example:
Movie 1: With roughly 30 years of peace since the Empire fell, among the ashes of the old, a new threat emerges. One with ambition to rise up in the power vacuum in the wake of the Empire's destruction. With followers of his own (of which Kylo Ren is included) they begin to make their presence known by proceeding to take over some of the Republic's territories. The heroes, Rey included, begin to sense increasing trouble. This would send Rey out in search of Luke, as he himself, who's been living a secluded life, he too begins to feel a trouble disturbance. And begin the movie with something other than a desert planet to start with. And seriously, leaving the whispers of the growing threat to the very end with the 3rd movie I felt was a mistake. Put something like it at the beginning and it would make more sense.
Movie 2: By now, we see Kylo Ren has ambitions of his own. Perhaps learning of his lineage makes him cocky, but in his own way, he wants to honor the memory of his Grandfather. Seems this new Villain and him don't always see eye-to-eye, which over the course of the movie, we see rising conflict, with an eventual confrontation towards the end which almost leads Kylo Ren to kill him and usurping power. Meanwhile, we see Luke training his new student Rey, although he never thought he'd be training anyone again after already crossing paths with Kylo Ren once before (Yes, some things stay the same with my idea). Meanwhile, despite our hero's best efforts, the new order is only growing bolder and more organized with their attempts to bring back darkness out of the shadows.
Movie 3: By now, our heroes are facing quite a considerable threat which is only growing more powerful, but they also know more about him and what he plans to do, and they are racing to get the upper hand. Our heroes are also fighting alongside some old and familiar friends along the way, including Rey who's got some new skills to show off. As our villain is at the crux of his plan, Kylo turns on his master, telling him he should have killed him when he had the chance. It's then that alongside our heroes, Kylo vanquishes his master. Kylo turns to Rey, and you can still see the anguish in his eyes, uncertain at what he'll do. They circle around each other, Rey trying to talk him down, and eventually dropping to his knees with exhaustion and dropping his saber, Kylo he admits to being defeated and not having the heart or will to oppose them, also admitting that he never truly felt like he belonged among the new order.
Now, see, these are broad strokes and all that and they're just ideas that are not very well developed, but I think seeing something like this would have been more satisfying.
