You just answer your own question!
Since politicians will cheat democracy, they will use the system to ban people running for office that threaten their power.
That's the concept of the separation of powers. Of course judges will have opinions and can never truly be objective (no such thing exists anyway), but their main job is to apply the law. And the concept of appeal and (in France) "cassation", which meana judgment can be revised up to two times, are there so that no single judge ruling can be definitive in isolation.
If politicians can use the judicial system to ban political opponents, the system is broken and powers are not separated in the right way. And I'll definitely not say that France has a perfect separation (the president concentrate a lot more than it should), but it's still there and this wasn't such a case (in the past two years, Le Pen and the RN is the group that Macron has been willingly compromising with and letting arbitrate a lot of stuff)
But judges don't determine which cases they will hear, prosecutors do.
You could have 12 people violate the law, but if the prosecutor decides not to pursue 11 of them, only the 1 will face any consequences.
US code is comprised of tens of thousands of laws. It's not hard to find one that you've violated at some point in your life.
Most of the time they aren't prosecuted. But if they decide to, a judge will have to find you guilty.