A poker machine hits the jackpot the same way it hits any combination of symbols – winning or otherwise.
The Random Number Generator inside the machine which is controlling the spins chooses the number that represents the jackpot. It makes this choice completely randomly.
The poker machine does not hit the jackpot because it is “due” to hit the jackpot. It does not hit the jackpot because of any skill or strategy on the part of the player. The machine hits the jackpot purely and simply because of the numbers that were randomly generated by the machine.