Keep in mind that inflation ran over 7% annualized in April [1].
Everything else is up around 3% YoY. And if energy and transportation are up double digits, and producer prices are up double digits, other consumer prices will follow.
The faster your cash loses value, the stronger your incentive to trade it for something else. That something else can be financial assets.
> It's not got loads to do with large-scale, institutional investments
For investors, particularly retail investors, the consumer price index is most relevant. But for whatever it's worth, producer prices are up over 16% in April (7% excluding "foods, energy, and trade services," which jumped over 50% annualized) [1].
To be clear, I'm floating a hypothesis here. I have seen no evidence linking inflation to demand for these companies' shares. (If anything, it should be the inverse.)