Because it ' s really expensiveNo it isn ' t as I have explained because you can either have government capital which you can leverage up like a private bank meaning you only need 50100 billion of capital for 500 billion of investment in assets , or you can do what Varoufakis argued for which is capitalize the Investment Bank with central bank funds this costs the government nothing . Similarly with Labour ' s plan for the half a trillion that requires economic boom to pay it back . This is also not true as you use the bank to invest in assets , the bank works like a private bank , they will have 500 billion of assets and 500 billion of debt , the bank can sell some of the assets or make money on the interest on these assets . So just like a private bank the net debt is 0 or the original capital so maybe 50 billion . It is no different to a private bank creating 500 billion in loans over 10 years . You would not say the private banking industry loaning out 500 billion over 10 years would need an economic boom to pay it back so why would a public bank run on the same logic need an economic boom to pay it back ? They just need the things they invest in to maintain value or be able to pay a small amount of interest . Parliament has already said we need 485 billion extra in infrastructure investments over the next decade . It ' s a risky as fuck Government investments are probably the least risky investments of all . It is no more or less risky than private banks investing in government infrastructure and it is probably cheaper and more efficient .