The reason is a different exposure of the banking system to mortgages than to shares. In this respect, bank-based financial systems incur larger losses than more market-based financial systems during housing price busts, while the opposite is true for equity price busts.
This finding is corroborated by the fact that all major banking crises in industrial countries during the post-war period coincided with housing price busts. Other studies recently confirmed that developments in the monetary aggregates and credit play an important role for the development of asset price boom episodes.