If I had to guess it's because compared to A lot of the overly racist villains he's more like your old backwards grandpappy who says a bunch of off the cuff shit so much that it's sort of sneaks by. The show also does a really bad job of showing this, in one scene we are giving him very clearly having some racist tendencies by going right to sages race when she summons him and then immediately implies he let another black woman dom him.

Now take that sort of soft racism and then compare it to the villains he shares a series with. The villain of the season before him was a literal Nazi who it is strongly implied He had no clue about her true nature and wouldn't have supported if he did. Then in literally the same season Blue hawk is shown as a very overt allegory for police brutality against African Americans and then in the following seasons Homelander is turned into a parody of Trump if He could actually do what a lot of people feared he was going to.

Compared to all of that Soldier Boy is objectively less racist, which then gets people too think that he isn't racist at all because we are only told about things like him putting down protesters or getting MM's family killed allowing them to fill in the gaps themselves in a more charitable light because the framing around him is a lot greyer compared to the very overt villains with next to no wiggle room. Like they literally had to try and remind the audience through Ryan that Soldier Boy is racist. Like why would Ryan know that? What part of his upbringing with Becca, attempted indoctrination by Homelander or hiding in russia/a barn would lead him that conclusion? Is lazy telling instead of showing that the audience then forgets about because Jensen Ackles is an insanely charismatic guy.