Even though they hired a lot of the same actors, they undoubebly had a different director. Some actors probably just wanted to do different takes as well. It is what it is.
For the most part, I'm fine with the remake voices. They're not offensively bad, except for Andross. But I get the feeling that was more from a lack of editing in the remake's case, the Andross voice in the original is *noticably* altered in many places, with the most extreme being the laugh.