The competitors have gotten more expensive, and apparently they've sold enough that the "shovel cash into development and make it up on volume" approach has worked. Like, the Gripen's development costs are a fraction of the F-35s, so it should be cheaper both because of that and because of being built with less fancy technology. But the development cost doesn't matter now that everyone and their dog is ordering a thousand F-35s (and it certainly feels like it took a certain amount of "no-one ever got fired for buying IBM" to get there, but at some point being the industry standard is a self-sustaining position), and meanwhile the Gripen is more expensive to operate than it should be because... honestly I'd really like to see some answers on what kind of "cost disease" seems to have affected all "4th gen" combat aircraft over the last 10 years or so, but it's undeniable that it's happened.