Because they want to do business in the EU and they have a legal presence there and have to obey the laws of any country where they do business.

In essence this is no different than being caught smuggling illegal products. If they don’t comply they will either have to pay huge fines or have to get out of the EU, which would be a huge blow to the platform.

Other huge platforms like Facebook and Twitter are toeing the line in regards to EU compliance so if they have to be careful you can bet a smaller fry like Reddit will have to be.

The catch is that the bigger you are the more value you draw from a huge market, so they definitely don’t afford to simply drop out.