In an interview with GameInformer, Cliff Bleszinski tackles the question of "Why go with Baird?" as the main protagonist in the quaternary Gears title, Judgment. Bleszinski explained simply that, "He didn't have his story told in Gears of War 3."
Everyone else had their moments, Marcus, Dom, and even Cole, but Baird was the not-so-silent fourth wheel, and Epic wants to take advantage of that and give him his moment in the spotlight.
Adrian Chmielarz explains that we know who Baird is as a character in the current titles, but his back story has never been explored. They admit that Judgment isn't an origin story, but will reveal things about Baird that explain what made him who he is today and who he was in the prior Gears titles.
Moving from Marcus Fenix, the somber and solemn leader of the Gears saga to this point, to Baird, the smartass backseat driver, is actually a breath of fresh air. According to Microsoft data, Baird as the "lovable bastard" is the most well liked character in the Gears franchise.
Bleszinski believes that Baird is so beloved because his attitude resonates well with the humor popular in internet culture.
Via GameInformer