Fuel load is fairly easy to understand. They aren’t running on fumes, so the car is heavier and behaves differently.
Driving style – They don’t do 60 qualifying laps back to back in the race. They are driving to conserve their tyres, so they don’t have to pit as often, and not fall victim to the tyres “falling off the cliff.” There’s other things like fuel consumption and reliability that they have to consider. If you compare a qualifying lap to a race lap, you’ll notice that they are much smoother in their driving inputs (short shifting, tidier steering movements, less aggressive throttle application). While being slower than qualifying overall, this also affects drivers with cars that don’t have good balance in the car. While they may be able to push a car with oversteering tendencies in qualifying, they will struggle in the race to keep it from burning it’s rear tyres, and as a result will be slower.
Tyres – This falls into the above description somewhat. The driver may be able to get their tyres up to temperature to hook up one fast lap, but maintaining ideal temperature during the race is difficult. They can also struggle with tyre degradation, which is of negligible significance in qualifying.
DRS – In previous years, drivers were able to use the DRS on the entire circuit in qualifying. A quick car in qualifying may have been set up with more aggressive aero, which gives more downforce and more drag. They were able to reduce their drag during qualifying, but not in the race. Also, DRS meant choosing gear ratios was tricky. Often, they would gear the cars so that they were quick in clear air (using DRS in qualifying, and not using it during the race), but found that they would hit the rev limit when trying a DRS overtake in the race.
Track conditions can change significantly over the weekend. Variables such as track temperature, how “green” the track is (amount of rubber on the racing line, as well as absence of contaminants such as dust, dirt, sand, foliage – a particular problem in Melbourne – and water) affect how the tyre interacts with the surface.