Because they are not full steps. The bottom set in this image is full steps. Can you see the difference?
Question for the Jefferson folks...do coins like the one in the OP images have less than full steps due to strike, or due to die wear? In other words, if those coins were fully-struck, would they have full steps? I am not a Jefferson collector so am not sure. The first coin (1966) looks to have very mushy details in the middle of Monticello, more so than just a weak strike would suggest. The 1959 looks to have more detail, but I am just not sure how much is strike and how much is due to the dies.
Correct the center steps are what is being looked at. As far as the question on strike....one must look at nickel mintages. Remember the 5 cent coin is the work horse of our coinage.....look at 1964 alone mintages for both P & D mints were the highest. I've had 64 nickels where there was no porch...more less steps. Some dates due to the dies finding a full step nickel would be like having a winnig lottery ticket. A member here posted today about a 1939 FS nickel a 1939 FS nickel in 66 was valued at $1500. And a ms 67. Was $100. One will learn quickly when becoming a serous Nickel collector how prices are all over the map... Now a days the modern strikes are all full steps as so proof strikes thats why proofs are not given a full step recognition. What a lot of collectors don't know is the full story of the Jefferson nickel. As the nickel that won the design was never minted.....well not by the U.S. mint. I will post an image tomorrow.....but if this tweaks your interest google Felix Schlag and then you'll know the rest of the story......
Both of those coins are showing die wear/fatigue. But, to your question, a lot of it depends on the year the nickel was struck. Not only does the mint try to get more out of their working dies, that also holds true to their master dies. There are years the master die was transferring mushy details because it was overused. Other years the mint tried to get more out of the working dies, so they open the gap up a small fraction between die faces. AKA, weak strike. Then those years the mint makes so many nickels they just abuse the dies until they look like a mushroom. Well, not that exaggerated but they overuse the dies. So, when they do that there are more coins with less than full details between new die changes. To get full steps it needs to be a new die pair and the proper spacing between dies. Or hit that coin twice to bring out the details. Trying to complete a Jefferson set with all full step coins would be a very major undertaking. And take lots of money.
Here's a thread that describes what a Full Step is (requires at least 5 full steps) : https://www.cointalk.com/threads/th...erson-nickels-defined-photographically.49827/
