From Czechia (based on your name)? Why so long?
* Pauses are required.
* Some roads cannot be used by some vehicles and/or cargo, especially in the Alps. Same with tunnels.
* Some countries ban trucks from their roads on certain days and hours, so a day off whether you want it or no.
* Sometimes your employer tells you to avoid some extra expensive road even at the cost of longer driving time. (Europe has a myriad of toll systems.)
* The cargo for the return journey is usually not ready on the same day, might well take five.