They are very unlikely to risk their time and money on a new voice, who may take 2 or 3 times longer to read the same script.
Time is money and often clients are incredibly busy and can't take 3 hours of their day to just listen to a voiceover recording.
That's not to mention the cost of the studio and engineer.
It would work out cheaper to pay an experienced professional to do a job in one hour than to pay a newbie for three hours with the cost of three hours studio time. Let alone 6 hours in the edit!
Very few voiceover artists work full time. They may also act, direct, produce or broadcast. You don't have to work full time as a voiceover artist to be a professional - you just be experienced.
