> You have to explicitly refuse any cable service from your ISP in order not to pay it

Legally, you have to pay if you have a television in you home and you are subject to paying the residence tax (which will soon be applicable to less than 20% of homes anyway).

> And it's significant

No, it's not. It's like less than 0.5% of the tax you are paying (considering income tax, social tax, residence/homeowning tax, VAT...). They just keep it because they can rile up /distract people when they increase the TV tax by 5 euros.

And it is a way for the government to pressure public TV/radio into some obedience (since the government can basically cut a large part of their funding of these TV/radio by removing this tax).