Really good.

You are quite right in describing the zero interest rate as central banks taking the foot of the brake. Similar to how a brake can decrease speed but not increase it, the interest rate can destroy demand but not create economic activity.

The reason for not using tried and effective method of Keynesian spending is of course ideological. In the euro zone it was ruthlessly enforced by the ECB and the Commission were the deficits created by automatic stabilisers were taken as breaking the Maastricht treaty and those countries had to be put through austerity.