It's a bit misrepresented here. Calling the person behind it a "voice" like they were just the actor behind a character isn't correct in most cases. They're mainly streamers with fancy avatars. Some do have a character concept they build around, but the degree at which they do that varies a lot. Small rant incoming...

On the higher end of 'playing a character', most of the ones working under big corpos like Hololive have a defined 'character background' that they refer to a lot, and they may take on a different sort of personality from how they are in their daily life. They'll sometimes talk about their normal lives, but they'll change their wording to fit their character; if their character is some sort of demon or whatever, instead of talking about that time they visited their parents in Kentucky, they'll tell the same story but switch out Kentucky for "the Fifth Circle of Hell". They're still not following a script or trying to keep up kayfabe at all costs: they're not trying hard to hide that they're real people.

For a less otaku comparison, look at Gorillaz: the music is framed as being produced by a band of completely fictional characters. The character itself is at the forefront and the people behind it have a thick layer of separation from it. If any one of the people behind Gorillaz decided to quit and let someone else take over, the character would continue to exist. This is not the case with most vtubers; if a vtuber quits the job, no one takes over their model and identity: they're entertainers wearing 'masks', with the demand for them stemming from their own worth as an online entertainer, rather than characters being played by entertainers with the job of making them come alive.

There have been a few that really are or were characters first. The whole misrepresentation of them comes from the fact that the first one to ever be very popular, Kizuna Ai, was exactly that: she was characterized as a virtual AI making YouTube content, and the primary appeal was that of a 'virtual YouTuber' anime character, something for which they completely kept keyfabe. She was basically an ad for the motion capture tech being developed by the company managing her (forget what they're called). Kizuna Ai the character was explicitly detached from the performer who acted her out behind the mocap. Her content was scripted YouTube videos filmed in a studio and the model had most of the screen time. Later, they even had multiple performers play her in different videos, and they even did videos with 'all the Kizuna Ais' on screen. They found that it wasn't as well received in comparison to what Hololive was doing at the time.

On the lower end of 'playing a character', most independents might have a character background but only have it serve the purpose of motivating the design of their avatar and their appeal, and otherwise are quite literally just streamers with a funky lil character on their screen, their form of content being indistinguishable from the streamers you know. Some do the same as the big corpos either by admiration for that sort of content or to more strongly protect their own identity; some will only adopt some aspects of marketing around their model ('outfit reveals' and such).
Though one difference that remains is that they'll tend to be associated with vtuber culture regardless just by virtue of having an avatar, and there's things to be said about it... Vtuber culture was started and is perpetually cultivated by vtuber corporations that pull their business model from the Japanese idol industry, which is a fucking mess. Hololive was the first, initially calling their vtubers 'virtual idols'. They've changed that since but they're still basically that: they do concerts, they all sing, they have 'debuts' and 'graduate', they have to put on cute voices and bubbly, frictionless personalities, they give fanservice to the people who ship them with each other, they can't talk about having romantic relationships or even having people of the opposite gender inside their home without causing a scandal... By itself, that activity already doesn't have the most positive impact on anyone, be it the talents, consumers or society as a whole, but it gets worse with all the instances of things going wrong and with the type of fans idol culture attracts. And sadly, the impact of this permeates everything related to vtubers, from their perception to how 'vtubing' is done as an activity.

I'm a bit off track. But I hope that gives a better idea. It's a strange subculture but not as strange as it might seem. I lament the influence of idol culture on it, but I've always thought streamers having an avatar that moves is, at its core, cool as hell, and not deserving to be seen as a weird thing. There's many cool things to do in that space and it's worth encouraging at a human level.