That is not only related to privacy regulations. Many European countries are not so consume oriented and have less spare dollars etc.

For example, iPhone market share was still at 26% in Europe. We have different consumer behavior than the US ... and that you can realize in these numbers.

Privacy regulations no doubt play a role but I would imagine there are other reasons too.

For example, while services in the US can reach the entire country using one language, EU is far more splintered (and not just with respect to language). That is to say, we have way more local services that only target the market within a country. For such services, it's hard to justify as much ad spend as you might if your potential market included hundreds of millions of people.

I imagine Europeans are also more reserved about buying from small vendors in another EU country than Americans would be about buying from another state. I think some EU countries even have a reputation (undeserved or not) for being "sketchy." I've seen lots of sellers who refuse to ship to Italy, for example. I've seen people wondering whether the cheap car part vendors in Estonia, Latvia or Lithuania are trustworthy..