’Them' doesn't really cut it as it's not clear if it's plural or singular.
Beyond the other reply about the history of the singular “they,” we also have another prominent plural pronoun we use in the singular all the time. So often we don’t even think about it as being plural anymore. So much so that we’ve created new plural versions of this already plural pronoun.
“You.”
“You” was originally the objective case plural 2nd person pronoun in English, with “ye” being the nominative.
But “thou” was considered informal, like the German “du” or the Spanish “tú,” and the plural 2nd person was used as the formal. And this eventually supplanted “thou” completely.
And now we think of “you” as singular to the point where we make slang words like “y’all” and “yous” to have a plural.
It's hard to force language to evolve in a specific direction.
Beyond the other reply about the history of the singular “they,” we also have another prominent plural pronoun we use in the singular all the time. So often we don’t even think about it as being plural anymore. So much so that we’ve created new plural versions of this already plural pronoun.
“You.”
“You” was originally the objective case plural 2nd person pronoun in English, with “ye” being the nominative.
But “thou” was considered informal, like the German “du” or the Spanish “tú,” and the plural 2nd person was used as the formal. And this eventually supplanted “thou” completely.
And now we think of “you” as singular to the point where we make slang words like “y’all” and “yous” to have a plural.
It's hard to force language to evolve in a specific direction.