Each bet on a progressive game diverts a slice into the pot, which is why the jackpot climbs in real time and why the return you experience while not winning it is lower than the game's headline RTP: part of that headline lives in a prize that almost nobody receives.
The chance of the top prize is of the order of millions to one against, and it is identical on every spin, whatever the pot's size. A larger pot improves the value of the jackpot without moving the probability of hitting it, and a freshly won pot resets the value, not the odds.
Why it matters
Progressives are marketed on the size of the number, and the number is real. What the marketing omits is that the jackpot is funded by the players chasing it, and that the base game underneath is more expensive than its non-progressive equivalent.
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