No, the laws are different- and more consumer friendly in the US- so the US consumer behavior is different.

Back when credit cards were first starting out (which happened in the US) the US Congress passed a law- the Fair Credit Billing Act of 1974- that consumers were only liable for $50 of losses as long as they reported the missing credit card within 60 days of the end of the fraudulent billing cycle. This was back when credit cards purchases were all made on paper with the machine that went "kachunk" and transferred a carbon copy of your card- everything was done completely offline. That law has not been changed, in fact, most banks completely waive the $50 and don't hold card-holders liable for anything reported (basically, annoying a customer over $50 isn't worth it to the bank). Thanks to the internet, suddenly cards got a lot easier to steal and a lot easier to exploit- but banks are still on the hook for all losses reported within 60 days of the end of the cycle. The result is that American banks have invested an enormous amount in real-time monitoring of credit card transactions, and are doing lots of stuff to monitor this- they care deeply since ultimately they are on the hook- but the consumer doesn't care. This is why US card's from the consumer perspective are so much laxer, because our banks have invested far more on the back-end because the consumer is held harmless in a way they aren't with European cards.

As a totally separate issue, the EU has regulated the amount of interchange fees that card-companies can charge, but the US has not capped them. The result is that US card-holders can get significant kickbacks for using cards (especially true for the top decile of wealth), in a way that is functionally impossible with EU issued cards that have capped interchange fees. There is a big lawsuit happening now to try and allow merchants to only accept low-fee cards (the standard VISA/MC/AMEX deal requires treating all cards equally, which gives them an incentive to push people to higher interchange cards). We will see what happens with that suit, but until then, American high-spenders can have much higher rewards on their cards, which also encourages greater use of the cards- and making them have less friction than the EU versions.

This theory explains why cardholders in the US are still using cards despite these being relatively less secure than in other countries, but fails to explain why issuing banks wouldn't take steps to protect their own fraud losses, such as introducing 3DS or PINs.

The actual explanation lies in the game theory of fraud prevention; see my sibling comment for details.

Why would the law being different mean they wouldn't use 3DS though? Surely it'd cut out a good amount of fraud along with the realtime monitoring? I understand that US consumers don't have a stake in this, but can't all the banks just agree to enforce 3DS? I can't imagine Americans are going to stop using their cards because of a small amount of friction added