Why does he keep using that same, crusty, old, nearly-broken camera you ask? Simple, because he couldn't afford to get a new one.
Though, he'd never admit that to anyone. His excuse, was that he was too emotionally attached too it to replace it. Which was a half truth. It was the first ever camera he's ever gotten ever since he started photography, after all.
But, it came with a lot more cons than pros. Well, the only "pro" about the camera was that it was Prompto's first camera. Other than that? Nothing good about it at all. He had to keep putting the lenses in after it pops out, and it would take forever for the pictures to load.
"Nah, this old thing is fine! Just gotta pop this back in and we're good to go!" Prompto said as he attempted (unsuccessfully) to get the lenses back on. God, he needed a new camera.