Dumb Question Of The Day

I do not think it has any thing yo do with centripetal....or centrifugal force.

The reason is more simple. The 'C' type circlip or snap ring with a circular cross section is not as secure in it's retaining groove as a rectangular section snap ring or spirolox.
The piston pin 'hammers' the retaining device & a round circlip in a round bore is easier to displace than a circlip with a sharp edge. Another contributing factor to round section circlips moving out of place could be insufficient depth of the machined groove.