Majority of the people who are saying this are Arab-Americans. They know how bad Trump will be, they voted overwhelmingly in favor of Biden back in 2020. Unfortunately, after a year of witnessing their entire ethnicity being written off as an acceptable casualty in the name of international diplomacy and foreign lobbying, they've become numb and just stopped caring. There have been repeated instsnces of Democrats actually silencing them from speaking up as well. They've adopted a scorched earth mentality and are deciding to send a giant "fuck you" to Harris and the entire Democratic party.
And the Democrats are also allowing Israel to do whatever they want. There's not much of a difference between the two on this topic.
2/3 Americans support enforcing a ceasefire. 80% of Democrats support this. She wouldn't lose nearly the amount of votes people claim she would if she were to take a stance. She would just lose out on the lobbying money from AIPAC and other pro Israel lobbyists.