Explaining the skyrocketing of US Equities

Hello fellows,

I would love to comprehend the mecanism that has pushed the US equities markets into the skies and will try to generate a quick explanation from what I do understand in this very day:

The FED has chose that the keep the rates low.
The investment and speculative banks do borrow money from the FED and the ECB in a price close of 0 plus they rejinject this cash on the financial markets.
The US and European firms do exactly the exact same to buyback their own stocks in volume which affect others to buy them too at a higher price.
The poor retails trader do market these markets and receive absorbed by iceberg orders in the big hands.
Brokers do nothing to assist these to understand what happens here so that many people loose cash.

Will there be an end to this rally when the FED ECB continue to provide the market with reduced cost cash, mountains of liquidity at reduced price?

How do traders can by Amazon or Apple at these levels? Are they .... Dumb?

It's 9 years the SP500 didn't retrace. If there is one, the back to reality should be violent. .

Thank you for your kind precisions.

LS