Most of the free wheel has a winning percentage like this which is 90% to the smallest reward then distribute the 10% on other prize on the wheel. Typically the jackpot winning percentage is 0.0000000….1% which is close to impossible to win.
This is what I hate on wheels. They should just put a small medium reward and distribute the winning percentage proportionally rather than put a huge amount while the smallest reward dominates the result of the wheel.
That's why it is called by jackpot because the chance to win the biggest reward is so small. This is also type of marketing strategy in order to make players to spin the wheels as many as possible because I am quite sure that many people are attracted to spin the wheels because of the possibility to win the jackpot although they are aware that the chance is small. Since the wheel is just a bonus, do not hope too much, it is better than nothing imho.