Are the polar vortexes main cause of ozone hole?
To blame ozone destruction on the polar vortex would be like blaming trees for surface ozone production downwind of cities. Yes, nature is involved in the process, but nature is not the source of the catalytic pollutant that caused large change in ozone concentrations.
The polar vortex is a naturally occurring meteorological phenomena that has occurred for millions of years, and the ozone layer was fine.  The issue is man-made halogenated compounds that catalytically destroy ozone (e.g. CFCs) when polar stratospheric clouds (PSCs) form.  The stronger the polar vortex, the colder it is and the longer the PSCs stick around, allowing more destruction of ozone.  The continental ice sheet over the south pole allows extremely cold temperatures, and so PSCs have been more prevalent there. Typically the Antarctic circle is much colder than the Arctic, so ozone destruction has been more prevalent in the southern hemisphere.  However, polar stratospheric clouds are occurring with increasing frequency in the Arctic.
I suppose you could argue that if there were no polar vortices, the ozone layer would not be so susceptible to CFCs.  However, the polar vortex and associated PSCs is a natural phenomena we cannot avoid.