Making a Sandtrooper first allows them to show off they're nailing the armor difference between the Stormtrooper and Sandtrooper right out of the gate. Plus they can reuse 80% of it for an eventual Stormtrooper. Plus like Luke: X-Wing they have more cool details to showcase the sculpting. Plus keeping the Stormtrooper back for future waves gives people something to anticipate. And shows that Hasbro has faith in the line. They probably also know they'll have to heavy pack an eventual Stormtrooper so wanna put him in a Wave with less popular characters.
I'm sure they will make Qui-Gon or Obi-Wan eventually. But Darth Maul is a more visually dynamic character.
And you're clueless if you think the line is D.O.A., as almost every forum is ablaze with excitement.
Even from people who would normally never collect Star Wars, because the don't collect 3 3/4".