Banks are hoding cash for the same reason as corporates. The cash is cheaply financed by low-cost debt and it has utility as an insurance-liquidity-pool-of-last resort in the case of a policy reversal by the Fed.
For argument's sake, assume debt is mis-priced right now relative to equity. If you believe that, and you are a bank, what you do is increase ROE through increasing leverage (shor debt markets+long equity). So, if you are a bank you borrow and buy back shares. Or, you borrow and keep shares at a minimum/flat.
On the other side of your ledger, if you are a bank and you believe debt is mis-priced, the last thing you want to be doing is going long credit (to customers). So, what you should expect is increasing debt/equity ratio and flat/decreasing proportion of long-credit/total assets.
The "stingy credit" allegation is perfectly rational if you make the assumption that debt is fundamentally mis-priced as an asset class. That is the essential assuption Wilson is making to explain why money is chasing equity/pe/vc.
The only open issue is whether or not the assumption is correct.
If we look at policy, when regulators ring-fence reserve and increase the reserve level, they are forcing the banks to sell-equity. The reason they are doing this is because--assuming equity is mis-priced--they understand that banks will leverage up. The problem with banks leveraging up increasingly over time is policy hysterisis.
If the fed policy results in increasing bank leverage, the baking system will become increasing more "brittle". This tie the hands of the Fed--when they move to revert policy--they will risk creating a problem due to having added "brittleness" to the financial system.
So, even the fed is acting as if the assumption about debt pricing is true.
That being said, it is a more difficult case to explain from first principles whether or not debt is truly mis-priced as an asset class. But the analysis can be followed as far as I can tell simpley based on the binary assimpyion (yes/no). And one of those assumptinos seems to explain alot, while the other faces a harder time making sense of the data we are seeing.
From your piece:
The hope is that the lower interest rates will encourage people and businesses to take out more loans and thereby start spending again.
What we are seeing is opportunistic borrowing for financial engineering. We are not seeing 1:1 borrowing to spending on operating expenses or PPE. We are seeing borrowing that is being spent on share-buy-backs and/or cash-stockpiles that maked increasing leverage ratios more operationally risk-tolerant. (And it seems this is true for corporates and financials, at least to a first order approximation.)