If people with non-"odious" views end up at such a platform, they will quickly notice the unusual concentration of "odious" views, and generally find it uncomfortable and leave. Thus there is a steady increase in the prevalence of "odious" views until they are near-universal on the platform.
I don't say this to excuse their actions or say that this filter is good, but that seems to be the fundamental mechanism.
Those whose focus is overtly offensive and oppressive speech, however ...