Def the shouting and screaming during long streams do not help. It's also not to say long hours of streaming can't develop anything other than throat issues. I remember Korone having to take a break for health reasons and it may or may not have had to do with how seditentary the job can be. That or like the ADHD Doggo she is, her mortal flesh couldn't take the strain of her energy.
I also wouldn't be surprised if diet and environment played a part. You'd be surprised what irritates your throat and by extent vocal chords. Too much salt, oil, spice, drinks or food that are too hot or cold temp wise, fizzy drinks, snacks that either turn into glass shards or sawdust (not tastewise but texture after you chew), etc etc. Air in the room too dry? Too humid? Hope you're a nose breather. I highly doubt smoking is a thing but maybe vaping (you never know when your oshi is a nicotine addict) or maybe family members and their social circles have smokers. Let's not forget allergens, industrial smog (I doubt any talents are living next to industrial machinery but you never know), and any other Vtuber activities they do that may or may not include more shouting, screaming, or talking outside of their usual streaming schedules.
As the Mechanicus would say, "The flesh is weak but the Machine is strong"
