It may seem like they aren't listening but make it clear that taking photos means a lot to YOU. Explain that photos connect generations and preserve the past.

Let them know you are documenting their life and they will appreciate revisiting those memories in the future.

If our kids take pictures, but those digital files never leave your phone or computer, your kids won't see the point of the effort put in. I had an idea years ago and it's made a huge difference. Every New Year's Eve I present my family with a slideshow that is a 

recap of our year. They see that all the photos I've snapped each month are compiled into something they can enjoy. They see the result of their effort. This can also be done by hanging photos on your walls or putting them in albums. 

I regularly send my teens text messages with old photos from their childhood or family events. I include captions or brief descriptions to provide context and evoke memories. 

Even if they don't respond right away, these messages are reminders of why it's so important to take photos along the way.