The most popular cultivars are from China, but there are also native American butterfly bush (Buddleja). I've heard the native ones support monarch's throughou

The most popular cultivars are from China, but there are also native American butterfly bush (Buddleja). I've heard the native ones support monarch's throughout their lives, but now I'm seeing that's not so - which would be odd... Why would Monarchs evolve to lay eggs where they'd starve?