Hey there Jeep-collector, I see that you're from silicon valley (San Jose area, right ?). If so, what beach were you trying ?
Most of the hard-core beach hunters around here wait for winter storms to erode the beaches. And usually detest dry sand hunting. If you've ever been in an area the size of your living room, and dug 500 targets, so fast that you can't even take a step in any direction w/o a dozen more 'beeps', you will never go back to dry sand hunting again.
When the beach isn't eroding, then the wet-sand inter-tidal zone will have very few targets. Just light weight stuff (caps) and/or whatever was only recently dropped in the last days or week or so. No fun.
But for those who ply the dry sand (or wet sand when sterile), no, I don't know why they'd be passing pennies. The only time I've ever seen beach-hunters get selective and pass high conductors, is when/if the targets on the wet are SO thick, that .... we begin to pass high conductors in our quest to up-our-odds are gold rings (which tend to be medium to low conductors, on-average).
If you google "Tom's beach tips", you'll see an article I wrote on the subject of beach erosion. At least in-so-far as it pertains to our central coast region.