Because I also drive a VW Up! with a 59BHP engine (1.0 N/A) and I think the engine is too weak for the car.
The issue isn't the peak power, but the torque curve. Small, naturally aspirated engines have very poor torque curves, which means that you really have to rev the engine to get the rated power from it. In real driving, where you're between 2,000 and 4,000RPM most of the time, the engine only makes at most 40BHP (peak torque of a meagre 80lb-ft doesn't come in until 3,500RPM). This is fine for driving in built up areas, but it's really bad when you need to accelerate up-hill on an on-ramp to join a motorway or build up speed on dual carriageways where there are roundabouts every mile.
The issue isn't the peak power, but the torque curve. Small, naturally aspirated engines have very poor torque curves, which means that you really have to rev the engine to get the rated power from it. In real driving, where you're between 2,000 and 4,000RPM most of the time, the engine only makes at most 40BHP (peak torque of a meagre 80lb-ft doesn't come in until 3,500RPM). This is fine for driving in built up areas, but it's really bad when you need to accelerate up-hill on an on-ramp to join a motorway or build up speed on dual carriageways where there are roundabouts every mile.