People have been brainwashed and legal systems have been paid and bought for to consider them as such, just like corporations have been whitewashed to be treated as "persons".
In any case, we regulate all other kinds of speech as well: explicit content, libel, classified information, cigarette ads, and so on.
Let's start there. Corporations being persons is a legal fiction to allow them to consolidate capital. Giving that fictional person human rights is abhorrent to humans. It is a crime against humans. It degrades us.
Shouting fire in a crowded theater is also speech. So is publishing a highly detailed plan for anyone to kill the president and usurp power. So is child pornography. There's a long list of precedents that free speech in America is not absolute.
And this is about Europe, which has never had an absolutist view of rights to begin with. In Europe, rights are seen as intended to be balanced against each other instead of maximizing an arbitrary set of them to 100%. You have the right to free expression (except in... most countries, so let's call it a theoretical right) as well as the right to not be preyed upon. Although it's legal to distribute chemicals, some of them are highly addictive so they're restricted. Same with social media.
That’s not even true in the United States (they’re ‘commercial speech’, which carries a still significant but lesser set of protections), never mind in Europe.
Ads are speech.