Upper implants and full fixed bridge fitted recently, unhappy with the appearance as the teeth are barely visible. (Photos)

Teeth only visible if I smile really hard. Dentists say they'll correct but they can't make the teeth longer as the bridge will become unstable. They've said that the problem is that my upper lip has "collapsed" with age so the only solution is to replace the bridge with an implant retained overdenture as that will take up more space in my mouth and lift my upper lip. Is what they say correct; my top teeth aren't especially long. Should they not have considered this issue before progressing?