The funds are committed under the terms of the deal (share price, things like board seats, and other details). There are legal obligations to provide it.

This is a common structure for large investments. It would be really inefficient for all of these investors and companies to have to have the money sitting in cash to do a deal and then transfer it into the company's bank where it sits and earns interest for years until they can deploy it.

Even VC firms who raise funds work this way. The capital is "committed" but investors don't wire all of the money over right away so it can sit in the VC firm's bank accounts, waiting. The VCs do what's called a "capital call" through which they're legally bound to provide the money they committed when requested, under the terms of the deal.