Being stainless steel or tin they are nearly impervious to saltwater damage. Another big plus. Going to the tackle shop to pick out a saltwater spoon is like shopping for soda in the supermarket. Lots of makers, lots of choices, lots of sizes and colors. For the same reason as soda too.
Spoons are cheap to make and so a higher profit item.
The choice of one spoon over another has to be decided by some design detail that gives a spoon an edge. Lets look at some examples. Then you need weight AND reduced wind resistance. Otherwise, all two and a half ounce spoons would fly the same. Generally, the narrower the profile, the further the cast.