Small piston-powered aircraft generally use 65% or 75% only for convenience.
However, large radial piston engines used on airliners of the past generally cruised at much lower power settings. For example, the Pratt&Whitney R2800CB16 engine fitted to the DC-6 had a takeoff power rating (wet) of 2400 BHP, but was operated in cruise at 1100 BHP, approximately 45% of rated power.
The reason was maxium engine life.
In addition, piston engine airliners were ALWAYS cruised at a constant power setting, unlike a jet which is cruised at a constant speed, ATC permitting of course.