It’s not your imagination if you feel like you’re seeing more ads for baby formula than ever before. Formula makers have stepped up marketing campaigns to grab a bigger piece of the lucrative, $5.6 billion formula market, after a severe shortage earlier this year shook consumer confidence, said Allen Sayler, an industry consultant. The months-long closure of Abbott Laboratories’ formula plant in Michigan, after complaints of bacterial infections in infants, eroded the Similac maker’s market share.