From source code history, it seems this behavior is a relic of a very
old limitation when the same object couldn't be both a Softbody and a
Collision object. In those times if somehow both modifiers were added
to an object, Softbody auto-disabled itself and buttons were hidden.
Now however there is no problem having both modifiers on an object,
so there is no point hiding the buttons. The same exact buttons are
available on the physics tab in any case.
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