If the coins look new you most likely have come across a coin spill/fresh drop.
If You have come across a coin/target line, coins usually are green/brown/black(especially silver, and often are worn thin/smaller.
Waves and tidal actions cause targets of similar shape, surface area and density to accumulate in a small area like a sifter/classifier. Some days you will come across quarters the same way other times zincolins. Many times you will come across parallel target lines - usually quarters will be closer to the surf, dimes will be higher toward the high tide line and zinolns will be the highest as they are the lightest.
One time I came across a coin spill of several nickles which was especially exciting as their tone is close to gold.
The denser the items you come across especially old sinkers (grey matter) the better as it indicates that the bottom is able to support gold rings and they may still be in detecting range.
I seriously doubt that the beach had been picked clean by all but dimes.
Usually, detectorists who cherry pick for gold at the beach will ignore high tones as they are looking for gold which is a low conductor. While detectorists who cherry pick for silver coins and jewlery (mostly in parks) will only dig high tones as silver is a high conductor. If all you detect is zincolins, it may indicate that detectorists are using a CTX 3030s and rejecting zinc pennies
If your detector is nulling you are dectecting in discrimination mode!
For a better understanding view surfdigger videos.
Brian has several excellent videos on this topic.
Okay seemed odd today was out at low tide in the wet sand, and I found dimes. I dug 6 targets found four dimes, that beaded key chain and a pair of Sun glasses..I was finding some of the dimes, 14 inches or better. ( my scoop is 14 inches nose to back). Using an Excalibur ii (ppm). But nothing else there where a lot used sparkler sticks, sensitivity was set at 2 - 3 I passed over many nulled targets. Not sure if that means the beach has been picked clean all but the dimes?
My thought is I must have good set up to find dimes...or it it just luck?