I think the reverse repo situation sheds some light on why this wasn't happening as much earlier: https://fred.stlouisfed.org/series/RRPONTSYD/
Put simply there's now a glut of money that is waiting to be invested via loans in anything that has a good ROI with low enough risks. In the past due to higher interest rates and various other factors (including regulatory) this glut of money just didn't exist before.