How a name acquires a certain widespread association or is considered usable vs. unusable will vary from person to person, but much of our views are shaped by the culture in which we live. We don’t declare a name to be taboo, outlandish, trashy, pretentious, heavy, old-fashioned, etc., in a vacuum.
In most Western languages, female names generally end in vowels and male names ends in consonants. Therefore, some people find it odd to encounter a male name ending in an A, as is common in, for example, Indian and Japanese names. Some people even co-opt male names into female name because of this, like the very male name Nikita. It’s one thing for a male name from your own language to gradually cross sex-based lines, like Ashley, Courtney, or Evelyn, but you can’t just appropriate a name from another language just because you think it sounds feminine and have no idea it’s only used on men in the source language.
All names have to originate somewhere, but invented names which became popular weren’t just thrown together from random syllables. They were based in familiar sounds and letters, and had solid etymologies. True, names like Miranda, Jessica, Vanessa, Pamela, and Wendy sound like names because we’re very familiar with them and they’ve been around a long time, but when they were invented, people had never heard them before. They were accepted as real names because of the way they look and sound. Would invented names like Rhagmutt or Zunker have caught on in a Western culture?
Some names we started out disliking or not considering real names become names we’ll give a pass to, or even begin to like, thanks to good personal associations. I, for example, have no problem picturing an adult woman with a formerly male-only name like Mackenzie or Taylor because I’ve encountered them myself. I also have less of a hard time picturing an adult Brittany, or a Brittany with serious interests. However, there are still certain names I just can’t picture on an adult, not only because I’ve never known any adults with those names, but also because they just have a very childish sound.
Some names which sound perfectly normal and lovely in the native language may cause English-speakers to laugh, like Dong, Dung, Bich, Yu, Yuki, Cowessess, Foka, Floor, Phuc, and Trees. They don’t know the pronunciation is different, or that it’s not considered laugh-worthy in the language of origin. Some English names have also gone from acceptable to taboo, or at least the butt of jokes, like Dick, Titty (a nickname for Leticia), Fanny, Rod, Buddy, and Gaylord.
Nevaeh-it’s-Heaven-spelt-backwards-TEEHEEHEE!-isn’t-that-the-cutest-and-cleverest-thing-ever?! fails as a name for me because it doesn’t look or sound like a name, beyond just the stupid etymology and very, very, very recent origin. While there are many types of established names in the Western languages, ranging from flowery (Isabella, Anastasia) to short and to the point (Brooke, Lark), Heaven spelt backwards doesn’t look or sound like a familiar, established name. Even the most common pronunciation doesn’t match English spelling rules at all.
Almost everyone will have some names s/he hates or considers taboo due to bad personal associations, but that doesn’t make them unusable for everyone. The names Bernard and Logan are poison to me because of awful bullies by those names, and by the time I met another Logan, who was nothing like the bully in junior high, the damage had already long been done.
However, it’s different when a well-known person’s name becomes taboo. Let’s say you really hated Bill Clinton or George W. Bush, depending upon your political views. The names William and George haven’t become taboo, because there are too many people with those names, and plenty of other associations. The name Adolf has become so taboo, so verboten, it’s even illegal in some countries, like Sweden. Who has any other association with Adolf/Adolph/Adolphe? I only know several other famous bearers because I’m a historian and lover of classic films. While it was far from rare, it also wasn’t exactly the most common name either. Hence, its almost complete disuse ever since.
The kinds of sounds we like in a name will vary from person to person, and we might like some names others consider cartoonish or fit only for fictional characters, like Midnight or Rhapsody. But ultimately, the names considered usable vs. unusable by the wider, general native culture follow certain patterns.