EU companies pay for advertising there. You know, their customers. They sell to customers in the EU. The social network/search thingy doesn't have any relevance to tax - it's their advertisement business governments want a slice of.

If there's any problem with taxation any country can order its banks to not process payments to Google/Facebook. Tax authorities don't give a shit who hosts the citizenry's family photos. That's not what "operating in" a country means.