the more characters you have in your alphabet the higher the risk of pairs that are difficult to tell appart
0Oo
1l
etc 0Oo
1l
etcAlthough it is true the potential risk may be higher, it is easy to find counterexamples where this potential risk does not matter. The 26 capital letters are easy to distinguish and allow you to use a base-26 system, while a base-2 system where the only two elements are 1 and l (or 0 and O) would be more difficult to use, for example.
Oo
Il