I've heard various stories on why Curry didn't get the part: it was difficult for him to maintain the voice well through an entire recording session, he was sick with a severe case of bronchitis, or the network brass decided his Joker sounded too scary for younger viewers. Let that 'un sink in for a minute--he was
too scary to play the [
bleep]ing
Joker.Then again, perhaps they had a good point....
They did, however, use some audio of Curry's laughter for a robot in the episode "
Be a Clown".