I read Trek books because I love to be able to just jump right into a story already understanding the universe I'm in. I already know the characters and setting, and have an emotional investment in everything. I really enjoy continuing to follow the stories I've followed since childhood as well. I wouldn't be interested in Trek books at all if they didn't continue the storylines after the series. These are the same reasons I read the Star Wars EU and a few other media tie in series.