For a musician, the honor getting to sing the James Bond theme song is in its own category. Many movies need songs, but you never see articles wondering who will do the next Fast and the Furious song (even though more people would likely hear your song there than in Bond). Giving their music to sell a product is something musicians regularly do, but rarely take as a career honor.
But given the track record Bond theme songs have had, the appeal makes sense. James Bond songs might even have a higher batting average than James Bond movies (and certainly higher than James Bond actors). And there’s a prevailing sense artists are chosen for abilities beyond just star-power, despite plenty of counterexamples over the years. Some of the most iconic songs were sung by singers who rarely topped the charts elsewhere – three by Shirley Bassey alone – whereas attempts to grab zeitgiesty performers have flopped.