Pretty much what the title says. After the revolution, he presumably could’ve gone back to using his birth name if he wanted to. As someone who also goes by a different name than my birth name, I have nothing against that, I’m just curious about what his reasons were.
I haven’t read anything about it, but I would assume (as I assume for Lenin too) that they kept the alias post-rev because people knew them by that name already. A name is just, ultimately, what people know you by. So it’s easier to keep using a name people already know, rather than transitioning people into using a new/different one.
I also use a name that isn’t my given one, in fact, I get enraged by the use of my given name (it’s a bad name that never represented me). But, I’ll let people who knew me before I changed my name to use my given name if it’s easier on them. Because getting people to use a different name can be frustrating. (though, thankfully, the people who actually gave a shit about me happily used my new name instead, and I’ve just gotten all the people who refused to change with me out of my life)
It probably just became who he was as a person.