"Overall productivity increases don't increase profits. They reduce prices! Workers make more because everything costs less."

That only applies in an economy without credit and where sales are constrained by the spending of the wage share. In an economy with credit you can use financialisation to give people spending power their wages don't permit, which keeps prices higher than they would otherwise be and allows more to flow to the profit share.

The dynamics then drives the path of interest rates down over the years until you get a credit crunch - at which point the lack of spending from the profit share suddenly shows up in a Minsky Moment.