Eurostar checks are very tight and even on busy days it won't take over an hour of queuing at Gare du Nord. Usually there aren't so many trains to board so it's much easier to organize. I suffered a whole station lock-down on a busy Sunday night due to a large piece of luggage left near the security checkpoint. It delayed my trip only 2 hours, including the delays of not being on time for the cleared route. Another thing is trains don't usually have busy schedule of airplanes so they usually wait for people if something like that happens.

Also there's no fuel around to use as explosive material.