There is also a "life" issue.
The hotter the engine the more power (until it melts !)
Also the hotter the engine the shorter the life on turbine components.
Many engines can be uprated and de-rated without any physical change to the engine.
Some engines use the same turbine part numbers in the higher and lower power engines but the higher temp (power) parts have a shorter life.
Aircraft operate in different enviroments, (hotter/higher) so rather than penalise the guy who doesn't need the higher perfomance the same engine has different ratings