I believe this is due to the differing contrast features of the planets. For example Mars has higher contrasting features than Jupiter and takes higher magnification better. Jupiter's features are more low contrast and are easier washed out by higher magnifications.
If seeing is the same and telescope / eye piece is the same , planets differ in the quality of view due to but not limited to a number of things …..,
How close the planet is to Opposition which affects their magnitude of Brightness
Surface Contrast of the light disc ( as per Epick Crom ) Mars tends to have more contrast between the poles and equatorial region just below.
Position in the Sky ( higher altitudes generally provide crisper views than down amongst the swamps ) Less atmosphere to punch through
Anatomical or biological make up and condition of your eyes ( rods and cones ) the eye sometimes can detect slightly improved detail from different wavelengths of light, particularly if your tired.
As we know seeing and transparency can change drastically within an hour or so during an observing session ( unless you live in a desert )
I would add apparent size. For example, changes in magnification for a larger object such as Jupiter will be more noticible in the eyepiece than changes in magnification for a smaller object such as Neptune.
