But why are MegaCorp (0.1 trillion and up publicly traded corporations) paying billions?
Largely, I suspect, to forestall competition and enable monopoly rent earnings. Incidentally sweeping up disruptive talent  as well as aborting potential corporate competitors.
We usually think of this acquisition bubble as driven by “paying you to borrow” interest rates, but it’s also being funded by the monopoly rents we pay oligopolies in the new gilded age.
When does it stop?
The ultimate limit is probably the ability of consumers to pay the rent(s)…
 Talent doesn’t have to be put to good use, just kept out of job market until threat expires. (*cough* secular stagnation *cough*). The corporate acquisition is intentional, the talent lock is partly an “invisible hand” class “happy accident”.