I'm going to omit marketing requirements in my answer (like the ability to put the localized name of the character into the company approved slot on a piece of merchandise, which is a big thing) and focus on the language.
Spider-Man is a man who is also a spider.
He literally "does whatever a spider can": climbs walls, shoots webs and eats flies.
Whatever name is chosen in Russian for him, it would better reflect this side of his personality.
Batman is a human who is somewhat into bats. He wears a mask with latex ears, drives a bat-themed vehicle and they use this bat-shaped silhouette on the searchlight to summon him.
This gives the translator some liberty: it does not need to say "bat" right in the name.
The name should work.
Человек-паук is a barely okay name: it's not too long, relatively easy to write and pronounce, and is a literal translation of the original. No one gets fired for being too literal.
There's a good chance that someone's nickname as a teen was "Spider-man" in the English speaking world, even before the advent of the comic character.
The chance of someone being called "человек-паук" on a regular basis, as a moniker, in Russian is slim.
So it's not that good a translation, but it would do.
Человек — летучая мышь is just plain unacceptable.
First of all, летучая мышь is a feminine name in Russian which means it would only work for a female character in storytelling.
Second, it's not something you can pronounce more than once. It's gonna be contracted one way or another.
Бэтмен is just shorter and it is the original. And no one gets fired for using the original.
The name should be catchy.
Some writers have an ear for things like this, others do not.
Человек-паук is not the best name out there, but it's catchy enough. Just by saying it out loud, everyone immediately gets who are you talking about.
Нетопырь and all other chiropteran names give the wrong idea about the character. This is a good name for a small minion to The Viy, not for a grim and troubled vigilante billionaire. Those just don't ring the right bells in Russian.
It's something that one can get used to, like everyone did with Человек-паук, but it's not the best option or even a good option.
All this requirements have something in common. If you can't come up with a really good name which would click, there's always a safe default way: just use the original.
There were many failed attempts to come up with a good translation for a foreign name or nickname into Russian which had since defaulted to the original: Румпельштильцхен (Хламушка, Гном-Тихогром); Рапунцель (Колокольчик), Оле-Лукойе (Оле — Закрой Глазки) etc.
I can't say with confidence that it's impossible to translate this name into Russian, but apparently it's not that easy.
There are good translations for Cinderella, Thumbelina, Snow White and Spider-Man but there are none for Rumpelstilzchen, Ole Lukøje, Rapunzel and Batman. Those from the last group have defaulted to the originals, and not because people didn't try.
So the answer to your question would be:
Not all names are made equal, even if they use the same pattern in the original language.
Spider-man works in Russian translation, Batman doesn't and he's in a good company.
Of course it may happen so that the minute after I post this answer someone would come up with a brilliant translation for Batman which would then get traction, become approved by DC Comics and make its author a fortune.
This would make me feel embarrassed but happy.
However, it didn't happen to lots of names and, from the looks of it, not gonna happen to Batman either.
