please explain qualitatively: why do electrons in a semiconductor have greater mobility than holes?

In semiconductors, current is often visualized by the flow
of electrons or positively charged holes from atom to atom in the
material.  However, only the electrons are actually free to move.  The
holes are positively charged ions that are created when an electron
leaves the atom.  The location of the hole changes when electrons leave one atome to
fill the hole in another one.