Vcs don't typically deploy capital that was loaned to them. VCs get their money from rich people and institutional investors and pension funds. They take their investment dollars and deploy it into startups that they think are winners. To help the startups succeed, these startups go to a venture debt bank like SVB to get a loan to extend their cash runway and limit dilution from subsequent equity rounds before they can cash out via an IPO or being bought. Not any banking going to underwrite a loan to a startup company. A lot of these venture bank loan risk profile are actually geared towards the VC creditability and relationship as a source of repayment, and not the startup.

Part of the requirement for these startups to get a loan is they must keep their cash with the bank so the bank can closely monitor cash runway to limit defaults.