For me the problem is that I'm not a great photographer. I take loads of bad photos. It would take me far too much time to go through all of them and decide which ones to keep.
Also, my wife and I sometimes look at old photos for reasons that have nothing to do with the quality of the photo or even with reminiscing. Instead, we may look for some specific fact (mole, dental issue, dress, haircut, domestic repairs, flooded footpaths, etc). The more photos we keep, the more likely it is that we can find what we're looking for.
For me the problem is that I'm not a great photographer. I take loads of bad photos. It would take me far too much time to go through all of them and decide which ones to keep.
Also, my wife and I sometimes look at old photos for reasons that have nothing to do with the quality of the photo or even with reminiscing. Instead, we may look for some specific fact (mole, dental issue, dress, haircut, domestic repairs, flooded footpaths, etc). The more photos we keep, the more likely it is that we can find what we're looking for.