The electronic configuration of copper is shown below;
[Kr]4d10 5s1
We can see that there is only one 5s1 electron. Hence Ag^+ tends to display a pseudo noble gas configuration. This pseudo noble gas configuration explains why silver is prevalent in the +1 oxidation state.
The other transition metals have many stable oxidation states found in nature. Chromium is observed both in +3 and +6 oxidation states. Iron is found in +2 and +3 oxidation states and copper is mostly stable in the +2 oxidation state since the +1 oxidation state readily disproportionate.
Hence silver tends to have only a single ionic charge for reasons aptly stated above.
