People complain all the time about being politically homeless, or muse whether they'll actually bother voting because they feel they're not being listened to, all the way from the most ultra pro-trans people through to economic leftists who nevertheless feel deportations to Rwanda might not be the worst idea ever.
The only question Starmer cares about is which tranche is largest, best placed and most likely to act on its complaints. In this case, given his most recent comments, he's clearly decided he'll lose less by pandering to the "gender critical" set. So they win, and he'll happily be throwing trans people under the bus until the maths changes.
(Edit: As a side note, for such people who believe in voting I'd say being willing to put their X in favour of Labour's stances on trade unionism, migration, welfare, protest rights, the environment, tax, nationalisation etc, then drawing the line at it being too wobbly on self-ID, not that it's pro but that it's not anti enough, is pretty damning).