If the Fed is committed to propping up equity markets which they asserted in no uncertain terms when markets died in the beginnings of the realization that COVID was going to be much more substantive than SARS or H1N1, it was clear that equity markets would take the "good news" of lockdowns + continued lower interest rates as signs that equity markets were going to continue to rally.
I mean basically where is there yield? Crypto + NFTs (yuck to the latter), real estate and equities. Even just running correlation analysis on these various assets over the last 20 years showed that crypto was super underpriced (despite only 12/13 year track record) while real estate is tremendously overvalued and equities were the only thing to react in a reasonable way to both (1) the initial realization covid was serious and (2) the Fed stepping in with 2 novel revolvers for SMB and for corporate credit. Treasury even threw in a bit into the bowl and performed stimulus. The last 1.5 years likely minted more "wealth" than in the previous 100 years combined (hand waving a bit) - a framework was laid to make much more money than what you put in provided you were looking at what was to come based on what was spoken.