EU has a LOT more truck volume (both in terms of per capita and percentage of freight shipped by truck). This has some complex and not so obvious implications on how long things get hauled. The smaller trucks also make it more economical to do trips between hubs vs hauling across 3000kms (which is reasonably common in the US). Smaller trailer capacity (due to EU length restrictions) and increased depot/truck distribution means a heavier distribution towards shorter hauling.

Also cargo rail is supposedly not a prevalent in the EU as it is in the US. (Vice versa for passenger rail.)

Last time I checked, the US was only slightly behind Russia in rail ton-miles.

Count it per capita.

Are there any routes in Europe as long as the US coast-to-coast haul?

Quick look at a map will tell you yes. Might not be as common, but I am sure fruit gets delivered to Finland from Andalucía by road.

But Finland has only 5 million inhabitants, so the volume is nearly negligible on European scale. The big population centers are closer to each other and even agricultural hotspots.

I'm sure trailers make the trip. But are they pulled by one tractor the whole way?

Yes.