WASHINGTON—JetBlue Airways said Tuesday it made an unsolicited $3.6 billion bid for Spirit Airlines, potentially snarling merger plans between the ultra-low-cost carrier and Frontier Group Holdings. JetBlue Chief Executive Officer Robin Hayes said the deal would make the New York-based airline a stronger competitor to the so-called four legacy U.S. airlines that control nearly 80 percent of the U.S. passenger market. “The number one complaint we get is why don’t you fly to more places,” Hayes said in a Reuters interview late Tuesday. “What we want to do is create a bigger JetBlue” that can serve more consumers. JetBlue, the sixth largest U.S. passenger carrier, would operate Spirit under the JetBlue brand and he does not think any divestitures are needed. The move comes as airlines face higher fuel and labor costs, and work to attract more leisure travelers, who have returned at a faster rate than business travelers since …