There are a few daytime flights to Europe from the East Coast of the US. But they are only useful if you aren't connecting onward as they arrive too late to catch a connecting flight. They also have to leave extremely early so if you have to connect to catch them it might not be an option. So basically they are reliant on O&D on both sides, a great option if you are flying NYC-LON, not so great if you are traveling somewhere else in the US to somewhere else in Europe. Remember at many airports there are curfews so they can't take off/land in the middle of the night.

It's also about aircraft utilization. It costs money to keep a plane on the ground. So the plane arrives in Europe from the US and then two hours later is flying back to the US.