A source close to Airey said she had become disenchanted with the opportunity after realising that Iostar was going to operate with largely venture capital funding rather than private equity.
This meant that management could expect to own a lesser proportion of the company and profit less from their endeavours.
"The problem with start-ups is that you don't get to see under the skin of the business until you go to work there," said the source.
"Dawn didn't leave a massive company like Sky to be a bit-part player in a new business."
Her departure now puts Airey, who left Sky in March, back in the frame for a number of senior TV roles.
Virgin Media, currently engaged in a bitter battle with Sky over carriage payments, would likely value her knowledge of the broadcaster immensely.
However, a move out of TV would not be a surprise.
Speaking to Media Week last year, Airey, a movie buff, said she envisaged a career move out of television into "entertainment in its widest form".
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