from a database theory aspect, nyms have greater uniqueness... like, if you just count the combinations, for all lower case 11,881,376 (same if all are upper) and for mixed case 380,204,032 which is a really lot of very memorable distinct names, let's say that 10% of those are intelligible

because "real names" sometimes are ambiguous this is a problem from this perspective, and partly why most social network systems rely on conflict free identity numbers as primary keys in databases

that is just in terms of practicality for the systems, the matter of being "autonomous" also has a big part in this, thus the conversation about agency - autonomous literally means self-defining as well as self-directing, and taking on a nym is an act of self definition