Because the volume is overwhelming, and dilutes the appreciation of the good ones.

I'd rather have 200 great photos than 200 great, 300 good, 300 ok and 200 blurred, dark, crummy ones.

I am probably the more enthusiastic photographer, but DH takes heaps too.

Between the two of us, we've taken almost 10,000 photos this year. It's just too many. It drowns you ...
I suppose it just depends on how you look at it - I have taken 17,627 photos this year (well maybe I have taken 17 000 and DH has taken 627) according to Picasa - which is above average because in the past 5 years it says 54,543 - but I take alot of burst photos these days so I suspect that is the difference). I would rather spend the time on editing those that I feel worthy, than working out what to cull - but I am not really a photographer - I am a recorder, the photos I like are not really that great photos - but tell some sort of story, they picture something, someone or a moment I feel I would like to remember in the future.

I suspect it might be like either loving or hating vegemite - either you can cope with lots of extraneous photos that might not be great, or too many photos makes you feel like you are drowning.