It seems that flexible objects just don't model well in many popular constructive solid geometry (CSG) CAD programs. Most CSG modelers seem to assume exclusively rigid bodies with sharply defined and constrained motions. Actually having fully dynamic unconstrained components seems mind-blowingly out of scope.
For example, there is a "collapsing string toy" from decades ago, that seems to be far beyond the ability of most CSG CAD to model and then dynamically simulate:
Google image search: collapsing string toy (also known as a "thumb puppet")
It is similarly exceptionally difficult for most CSG modeling software to accurately model and simulate the motion of a solid rectangular cube supported by two eye bolts, attached to two compound block and tackle rope pulleys.
It is very limiting for a mechanical engineer to be locked into such an inflexible and rigid understanding of modeling.
So, what CSG modeling software is actually capable of simulating such dynamic complexity of motion?