A book often associated with Clark. Jon's age up has been extremely unpopular amongst his fans. A lot of people aren't fans of at least some of the designs shown so far. A book that's had a LOT of issues in the past in recent years in trying to be an ongoing (tying back into Jon being shipped off to it). I could keep going.
And yet, that's whom they're most associated with.They've tried that as well in the past.
A lot of new readers also like to look up the past history of new comics. Look at the blowback the original Red Hood and the Outlaws got for sticking Roy and Starfire with Jason for example.I won't pretend like I *know* for a fact what will sell and what won't, but it seems to me that simple logic dictates that new readers appreciate the ability to have a fresh start with a property. No one likes to feel like they're missing something when they're trying to get into something new. Speaking specifically for Legion: one of the *number one* issues the Legion (like the X-Men, but without the aid of a multimedia force) face with getting new readers in is being a franchise with *literally* dozens and dozens and, yes you guessed it, dozens of characters, planets, and histories that the franchise becomes virtually impenetrable for anyone looking to get in. They are a team where having a couple dozen of them active at a time is considered small.
And each member has a corresponding back story, power, codename, real name, relationship status, possible children, relevant siblings or other family members, and home planet that can't possible be restated every single issue that character shows up, so you just have to remember it. There are people who have been reading comics for years and years that find themselves totally overwhelmed by the Legion's history, and thus skip it.