Well most common issues are the "Ride it hard and put it away wet" mentallity many use with their equipment. Im meticulous about oil changes, checking valves, fuel stabilizer, etc. Many people are too lazy and see a new motor as a cheaper and easier way to deal with motor issues.
Top End rebuilds(Piston, rings, honing cylinder walls, head work) and Low End rebuild(Cranks, Rods, other bearings) are a part of a motors life and are needed after extended engine life. Basic maintanece is key, and will keep a motor going longer than most expect.