Defund was probably a bad choice of word, and reform a better one ? But if people can only deal with single-word manifestos, then you re bound to misinterpret.
I think this is ahistorical. Progressives were pretty clear that they believed American policing was fundamentally, irredeemably, and universally racist--that was the whole crux of the BLM movement, and if you believe that, then you aren't going to content yourself with mere reform (if you think police are racist, then you probably aren't going to advocate for "requiring more training for dealing with mentally ill citizens" or similar reforms). Moreover, when moderate Democrats (fearing for the upcoming election cycle) tried to say "what progressives really mean is 'reform'", progressives responded with "no, we really mean defund/abolish".
"Reform" is too easy to silently crush. Oodles of police "reforms" have achieved precisely nothing at mitigating the widespread use of violence by police against the people. "Defund" argues that the institution itself is fundamentally broken and that we should be solving many of the problems that police are tasked with today through organizations that don't have the authority to execute people.