What is the reference interest rate for buyers of sovereign bonds in the euro zone?

The 10-year interest rate on all euro-zone sovereign bonds is almost zero. So why are there buyers of these bonds? We have to look at the reference interest rate, the rate against which purchases of public-sector bonds are arbitraged. For non-residents, it is the long-term interest rate in other currencies, especially the dollar, and which does not encourage purchases of euro-denominated bonds. For households and institutional investors, it is 0%, the yield on money (cash), which makes public sector bonds very unattractive. But for banks, it is -1%, the preferential interest rate on TLTROs, which explains why banks can buy government bonds as they have a positive carry on these purchases. The monetary policy implemented in the euro zone therefore drives banks to hold public sector bonds, which is inconsistent with the objective of decorrelating banking risk and sovereign risk.