If I'm not mistaken there is a tax on secondary residences in France. I am not an accountant, but my understanding is there is a "taxe d'habitation" from which primary residences are exempt, but which must be paid on secondary residences.

Of course, this can be gamed via starting a real estate company which buys the secondary residence, claiming that it is for "business purposes", but the basic idea of using taxation to prevent the accumulation of real estate by the wealthiest individuals is present.