Frontier Airlines has made a second attempt to acquire Spirit Airlines in a $2.1 billion deal, after an unsuccessful merger attempt in 2022.Spirit Airlines has rejected the offer, as it was significantly lower than the previous $2.9 billion merger proposal.The proposed merger would bring together the two largest budget carriers in the U.S. and could reshape competition in the airline industry.Frontier believes a combined airline would provide more options, deeper savings, and an enhanced travel experience.