I mean it's a nuclear missile, millimeter accuracy isn't really necessary. Somewhere in the general vicinity is good enough for it's purpose of going boom.
So even though Russia withdrew from START II almost immediately, the US continued to unilaterally remove the MIRV capability from its ICBM fleet and stick to single warhead Minuteman IIIs.
https://thebulletin.org/2017/03/how-us-nuclear-force-moderni...
Then they got a lot more accurate than .1%