ELI5: Why wouldn’t central banking always lead to central planning?

If a cartel of banks is loaning billions of dollars to existing firms to buy back their own stock – or even (don’t laugh) to invest in increasing production – what incentive do they have to finance a new competitor?

To what extent are mergers, acquisitions and consolidation a byproduct of central banking? Wouldn’t you ultimately end up with central planning after a long enough period of central banking?