Perhaps that's not the case organically but it seems that way because the media has been beating that drum relentlessly for the past half decade or so, in the process creating the actual strife they had been magnifying.

If you're genuinely asking, it's because:

- Race is immutable, and can't be faked

- Race is linked to genetics (ingroup preference increases YOUR genetic proliferation)

- For millions of years, we've done it this way (there were no class problems in prehistoric times)

It’s instantly apparent just by looking at someone, I would imagine. That’s at least part of it.

Class solidarity is non-existent in the US. Racial issues are much more visible. Poverty tends to be chronic and society to this day attempts to dismiss it as laziness or personal failure on the part of the individual, there isn't really anywhere for a flashpoint to happen. Incidents like George Floyd's murder act as a nexus around which debate, protests, and change can form.

History.

The history of the US is far more rasist then it is classist; and there has been far more social movements along racial lines then class lines.

While we have had (successful) class based movements in the past, there is no class based analog in US history to the civil rights movement, or abolition. Even school children understand what Martin Luther King day is about; most American's couldn't tell you what Labor Day is about.

When there was a global movement for class based solidarity, the US found itself on the other side of the fight. (I'm referring to cold war era communism).

Even if a class based approach makes more sense now; there is a lot of institutional and cultural inertia behind a race based approach.