You are right, I had the same thought. The only possible explanation is they mention they had all the actors record their lines for each episode in the recording booth together as a group. So they could play of each other. Which is uncommon in animation. So perhaps they thought having him record his lines separately would throw that off???
I got the Animated Series on DVD. There are more bonus features than I would have expected. There is an interview with Producers Bob Gale and John Ludin. Plus a separate one with many of the artists and animators. I was impressed to learn that many of them went on to very high profile jobs on films for Pixar and Dreamworks and other animated features. Also there is galleries of character designs, background paintings. Plus complete storyboards for 2 episodes.
I was 13 years old when the series first started. I saw and recorded most of the first season at the time. I only had seen a small number of episodes from the 2nd season before this.
It was interesting that while there was less time travel in the 2nd season, when it did happen it was mostly to Hill Valley. Like the actual movies. I think the only time that happened in the 1st was to 2091. But looking at an episode guide half of the 2nd season is devoted to time travel to Hill Valley in the 19th or 20th Century.
Of course two of the worst episodes, non time travel, are in that 2nd season. One where video game characters crossover into the real world and another in which the kids create a money tree... Both felt like poor knockoffs of Ducktales episodes.
That book mentions that CBS wanted all the science experiments dropped and an alien added to the cast for the 2nd season! But Bob Gale refused.