I hear a lot of reads that are very well spoken that really don't sound convincing. They don't really sound conversational at all. They are articulate but not "idea driven". I've heard casting agents on large project auditions describe it like this. "Nice voice, but doesn't mean it"
Advertisers tend to pick voiceover artists who can meet all the stylistic demands of the copy and still sound like they're just talking to one of their best friends. This ability to "personalize" copy isn't magic, it has certain musical characteristics.
When we are talking to people in our "Day Voice" we naturally use a lot of vocal change ups, "beat Changes" and deceptive cadences. It's part of the harmonic geography of how we communicate in daily life. When we read copy these characteristics are often left out, making the copy sound merely like a person just reading copy. It's important to study and retain these variations in our best natural speech and not loose that spontaneous expression when we are doing voiceover work.