Not the parent comment but in the Netherlands where I live you have to pay tax on your savings once it exceeds about 21K EUR.
The government then makes up that you must be at least getting 4% (up to 9% if you have up to 1M) interest, and it wants 30% of that interest of anything over that 21K EUR limit.
Meanwhile the current interest at banks is anywhere from 0.05% to 1% here (most major banks are around 0.2%).