Government aligned companies own the vast majority of the billboards.
This means both that a ton on public money goes directly to the pockets of the people in government, and that there are barely any billboards to buy for others.
Also if someone actually bothers them, they are not above sending the tax office to have day long inspections at the company dealing with the EU every week. Even if they didn’t find anything, the work involved paralyses the company. This has alredy happened a few times.