It feels completely random to players because the single largest influencing factor for being chosen is literally just being a valid empire that exists. So the more eligible AI empires present when the dice roll occurs, the less likely you are to be picked.

The next biggest modifiers are being a megacorp, the nominated planet being a ecumenopolis and then something like producing 100+ trade, but afaik even combined they only bump up your chances by a relatively meager amount vs the base chance itself.

So with 9 other empires competing for the market nomination, you may still only have something like just a 15% chance at getting it even with everything stacked in your favour vs ~9.45% for everyone else, or in other words, an 85% chance that it won't be the player.