I think I read/heard once that they wanted a warmer, more paternal Alfred than Revill provided. Not sure, though.
(I think one of the record-holders for getting replaced as an animation voice is James Avery. He was the original voice of Shredder on Teenage Mutant Ninja Turtles
, James Rhodes in the '90s Iron Man
, and Sir Bryant in The Legend of Prince Valiant
, and in all three cases he was later replaced by Dorian Harewood. I've always wondered why that was, since the two don't even sound that similar. And the three substitutions happened years apart, so it's not like he had to be replaced in all three roles at once.)