I know you said you were talking generally, but let me reply anyway; Warning, long post.
I absolutely ADORE the way Japanese sounds. I am constantly improving my language skills to be fluent in it. It just sounds great to me, this fascination started even before I understood one word of it, and before I got into anime.
English (my 3rd language) sounds good to me too, while for example German (my 2nd language) is on my least liked list, sound and grammar-wise. Russian (not part of the voicing, but my first language) I dislike grammar-wise, but like sound-wise. Especially swearing has much higher impact in Russian than every other language I know.
Coming back to why Japanese voice acting is superior for anime is because as I already said, the Japanese pour their hearts into voice acting and it's generally seen as a respectable job in Japan. In the West, pure voice actors are not really anything great. Or do you know anyone aspiring to be a voice actor when they grow up? There are enough young people in Japan who do.
And since Japanese companies don't skimp on voice acting, they also get voice actors who are known in their scene for being good. There are people who might decide to give a completely unknown franchise a try just because one of their favorite voice actors are voicing a character. I never heard of something like that here in the West.
Now, in the West, companies who import and localize for example JRPGs or anime, often want to do that with the lowest budget possible, and end up skimping on the voice actors. There ARE good voice actors in the West. Look at big movies getting localized, the voice acting is top-notch in German, for example. They even have set voice actors for big actors, so that one actor sounds the same across all localized movies.
But that's speaking about blockbusters with a huge budget. Anime never gets such a high budget, so sometimes the companies even end up using their regular employees who have no voice acting education to do the voice acting. Untrained personnel doesn't really contribute to the end product having a high quality, don't you agree?
Recently anime has been becoming more popular and budgets started rising as a result, so the chance to get a decent dub is rising as well. However, for someone who is already nearly fluent in Japanese and absolutely adores the sound of it... why would they risk getting stuck with a bad localization (meaning completely changed) or a bad dub (why does that girl suddenly sound like she's being f***ed in a normal fighting scene)?
Exaggerated examples? Not really. Take a look at ar tonelico 2, a pretty niche JRPG. In the process of it's localization by NISA, a lot of the scenes had their meaning changed, sometimes making the characters say stuff completely opposite of what they were supposed to say. And to make things worse, near the end of the game they even seemingly started using machine translation in some parts, maiming the meaning even further.
Let's look at that random fighting scene next. The reaction to getting hit/falling sounds somehow completely natural in Japanese (= impression of the person getting hurt). In English, the same scene had an obscene amount of moaning that didn't fit - at all (= impression of the person enjoying the situation, which obviously wasn't the case).
Another aspect of foreign dubs is that voice actors don't really care about pronouncing character names correctly. Or rather, they pronounce them applying phonetics of their language instead of keeping the original pronunciation. This hurts the overall impression for someone used to the correct one and is very distracting.
So, I prefer Japanese for things originating from Japan because it is the language the content was written in - no risk of meaning intended by the author being lost. If the content originates from a country which language I understand, I will try to watch it in that language. As a bonus, I also get all the unaltered puns and jokes, something that is insanely hard to localize without losing the meaning.
That should give enough reasons why I want to have an option to set voice to Japanese without having to change my client language. I know more about Japan than just what you get from anime. I'm not putting it on a pedestal and claiming Japanese can do no wrong, they're human like me and you.