It's an extremely pervasive misconception, but a model's voice is not really a matter of its training data, not by the time it reaches consumer eyes. The voice these models use are specifically selected for in RLHF, ie, curated by humans by telling it it did a good job when it uses this voice and telling it it did a bad job when it didn't use this voice.

Why do they specifically push for this voice? Because it is effective. This is "headline voice", the voice that gets people to endlessly click on Youtube clickbait and garbage articles. Most of the population gets a dopamine hit from this style of writing, making it legitimately addicting to them. Those who recognize it for what it is and find it insufferably grating are in a tiny, tiny minority.