Too little too late for many. Trust was lost in Starmer when he called the black lives matter [movement, not the organisation] a moment after performatively taking the knee, ignored the recommendations of the Forde report and ignored complaints of Islamophobia and anti-black racism within Labour.
Add that to him not seeming that different from a tory, he was already on thin ice and this would have only made up skeptical minds.
For some people, this is the final nail in a coffin that's been years in the making.