I think his disappointment stems from everybody mocking his Batman voice and not taking it seriously. Now it's a classic joke among people who say "I'm Batman."
When in reality, one of the most recognizable people in the world, on the level of Donald Trump, Bill Gates, or Mark Zuckerberg, would clearly need to disguise themselves beyond just what they're wearing. If I heard Donald Trump talking underneath a full Batman costume and mask, I would know it was Donald Trump. Same goes for ANY famous public figure like Jimmy Fallon, Kanye West, Stephen Colbert, literally ANYONE who's famous.
You can't just be a billionaire playboy and put on a mask and that's it.
The BvS/Arrow approach with the voice changer has always been the way to go in my opinion, but Bale completely nailed everything he did.