Probably because that's not the only possible interpretation of the issue.
I agree that in some instances, white seems to be primarily used as a synonym for bright/light, and black as one for darkness, shadow etc., such as in the case of white and black box testing.
However, other cases, such as "whitelist" and "blacklist", seem more nefarious at least in some cultures: A list of names, one of people to grant access to some service or facility, the other to be denied...
And as somebody else has already noted, for somebody without that cultural background, it might not even make any sense, unlike the much more self-describing alternatives "allowlist" and "denylist".
If there is an alternative available that is both more straightforward and that has less negative connotations – why not advocate for its use, and assume that those that do so do it out of good intentions (while at the same time not assuming that people using the other terms do so out of a desire to cause harm)?
The main problem seems to be that, as in many such cases, a nuanced discussion of the topic does not fit into a tweet or news headline, nor a Slackbot autoresponse, and least of all into a grammar checker.