I would say that anyone who is interested enough in something to participate regularly in a forum on the subject has an obsessive personality to some degree, so it's not surprising that we all like to collect / accumulate things. I think magazines are a relatively cheap way to keep adding to the collection, and before we know it, we have a rifle's worth in value of magazines stored in crates or on the shelf. I find the different magazine designs interesting, so I have a variety of them even though I mostly use GI mags and PMAGs. I have some of the colored Lancers too - not sure why, but they're just "neat" and different.
The reality is that even if they were banned tomorrow, none of us, or probably even our children, would ever need a hundred 5.56 mags. We could probably get by with 20-30 even in the most dire circumstances. Unless the world ended and we accidentally ran over a couple cases of them while backing out of the garage in a rush, they are pretty durable and will last a long time if they're not abused. But we like collecting them, and we feel better about having a bunch of them as "insurance."