Why are Smart car engines worn out so quickly?

Firstly lets get this into perspective. A 61bhp 599cc car is making 101.83 Bhp per litre which is very impressive, and the same specific power output as an E36 BMW M3. It is a little engine with only 2.7 litres of oil to cool and lubricate it. Most are driven flat out, full throttle everywhere, and often undergo poor maintenance. For example: sometimes only 3 spark plugs have been changed (they have 6: two per cylinder), they are given the the wrong oil and low grade fuel. There are many examples running high mileages and achieving 55+ mpg, but these have had a gentler life. Smart state in the handbook “Normal operation at constant speed 2000-3000rpm, brief periods of acceleration, e.g. when passing 3000-6300rpm.”