They provide a product in the EU, therefore they must either follow EU law or exit the EU market. Just like an EU company that provides a product in the US has to follow US law.
The line of 'following the law of another country' is grey area on the internet, given that it goes both ways:
EU online companies providing services to US users fail to provide the free speech guarantees that the US laws afford their citizens. That's because all EU countries have more strict laws limiting free speech. Should the EU companies break their own countries' law to satisfy the US audience?
Exactly what is "free speech guarantees" in the context of a private business?
So it seems there are states where a europeans social medium should abide by rules that would most likely contradict european laws, right?
Could you sharpen up this claim? Like suppose I run a microblogging site but I delete libellous posts and incitements to violence in accordance with my local European law. Am I violating a US law by allowing Americans to use the site?