Many people feel the show is well-written and interesting. It may not appeal to all viewers, but it is popular enough to still bring in enough money for the network to keep it on the air. Whether or not shows stay on the air is due to economics; not on the show quality.
No, How to Get Away with Murder should continue its run on cable television while fan base still supports it. The producer, Shonda Rhimes, has several long running series on the network television right now. Her fan base is enormous and continues to look for more stories from her production team.
No, How to Get Away WIth Murder should not have stopped after Season 1. Each season has its own plot, with an overarching story arc. It's a great show that appeals to a grown audience that has a desire to see not only a highly talented African American woman, Viola Davis, lead the cast, but a highly talented African American woman, Shonda Rhimes, as the producer and showrunner.
People like the show. It's not the kind of show that appeals to me, but as long as people keep tuning in each week and it keeps appealing to its fans I think it is a good thing that the show continues on the air. It has its fans and they appreciate it.