Mr Henare said there was nothing in the confidence and supply agreement or in Parliament's rules that said the Maori Party had to vote for the Government's choice for Speaker.
"I think their own fear got to them, that they were going against the Government."
The Maori Party co-leaders refused to comment about the matter yesterday, but Mr Henare said he was "gobsmacked" by the decision. He also continued his attack later on Twitter, describing the Maori Party as "cowards," "weak" and "scared."
Mr Key said several other people were also interested who had not been as public about it.
"I've indicated that in the range of people [interested in it] he is not necessarily my number one choice. It doesn't mean he's not good for the job, it just means I'm spoiled for choice with good candidates."
Mr Key said the Government was yet to decide who to nominate - although the front runners are widely understood to be David Carter and Maurice Williamson.
Labour leader David Shearer said his favourite of the contenders so far was Maurice Williamson: "he's been in Parliament a long time, he's got a good sense of humour, he's quick on his feet, I think he would be fair."
Mr Williamson would not comment yesterday. Mr Carter is the favourite for the job - partly because he is in Cabinet and if he was made Speaker, it would open up a gap for Nick Smith to return.
Mr Carter said yesterday it would be an honour to be the Speaker, but would not say whether he would prefer to stay as a minister.