Europeans are "used to it".
Not wishing to be rude but American non-servicemen have had it "soft" until 9/11 - let me explain. And frankly the Brits have not had it as tough as the Europeans.
Two generations before mine we had WW1. Northern France and Belgium were quagmires of death and destruction as was what is modern day Poland on the German/Russian front. Paris was shelled by the Germans, London and the East coast of England were bombed by Zeppelins. For the first time civilians were involved. The USA civilians had no such terror. Even their entry into the war came two an a half to nearly three years after it kicked off.
In the generation before mine we had WW2. European civilains stuck in the middle like never before plus the Holocaust. France decimated again; UK blitzed as far west as Plymouth, Belfast, Bristol, Cardiff and Liverpool. London got V1 and V2 weapons fired at them just after the Luftwaffe went on the back foot. Germany bombed flat. Russia and Poland utterly devastated as far as Moscow and Stalingrad. Italy rolled back as the US and UK pushed the Nazis back over two years.
Spain had its civil war just before WW2 and Greece had its civil war just after.
1950's through 1980's Europe is getting used to the idea that if WW3 kicks off they will be in the path of the USSR and any retaliatory action; nuclear weapons hang heavily.
Now let me swing to the UK.
Late 60's through late 90's - the ever present threat of the IRA and to a lesser extent the UDA response. Bombs going off in Northern Ireland, London, Manchester, Bristol.
Then suddenly we get 9/11. America wakes up. and since then it has been Muslim extremists at the fore. 7/7 in London 2005 then France seems to be at the forefront and now it is North West Europe once again.
We are "used to it" - have been for 100 years - it doesn't occur to me not to go to Europe due to terrorism. I've been to France, Belgium, Spain, Italy, Hungary, Switzerland - Mediterranean islands. Again it would not even occur to me not to go anywhere in Europe due to terrorism.
Going wider afield ... A JW elder in 2005 said to me "I wouldn't go to Bali - they had a bomb out there!" (referring to an incident in 2002 where over 200 were killed by Muslim extremists)
I sat in the hotel lobby of a Balinese hotel sipping pina colada watching one of these new-fangled flat screen TV's as the 7/7 bombings of London were reported.
All my life I have gone to London - school trips - Museum trips with my kids and now myself. Weekends away. Stop overs waiting for aeroplane journeys.
It doesn't occur to me to not go about my daily activities due to terrorism.