They've pinned their hopes on her, because who else can they turn to? If your priority is campaigning for an end to the genocide, then of course you'd say that.
Sadly, her national security advisor just tweeted this today, so I'd say those of us who predicted Harris would just take Biden's policy and give it a more sympathetic face are already looking to be proven correct:
Less than two weeks before he dropped out, he wrote an open letter to congressional democrats in which he wrote:
Unless this was all part of an elaborate hoax, it's clear he had no intention of dropping out at that time.