And for Italian and Spanish banks, in today's febrile climate there is a strong temptation to put any spare cash on deposit with central banks, even for a guaranteed loss on that money, because they don't want to double up on lending to households and businesses struggling to repay what they owe, and they don't want to beshortofcash if capital flight intensifies.
This does two things in the short run: it decreases the amount of bonds available to be owned and increases the amount ofcash in the hands of investors.