Quoting AWS's literal rationale:
> Recently, we’ve seen a steady increase in this violent content on your website, all of which violates our terms. [...] This morning, you shared that you have a plan to more proactively moderate violent content, but you plan to do so manually with volunteers. It’s our view that this nascent plan to use volunteers to promptly identify and remove dangerous content will not work in light of the rapidly growing number of violent posts.
Whether AWS was able to make that decision because of the political calculus had changed (e.g. there was demonstrable evidence of real-life violence stemming from plans made on Parler; others had taken action against Parler; AWS's employees were publicly calling for Parler to be removed from AWS) -- that's a different question.
The timing can be political but the decision apolitical.
This is ignoring that Parler's continued prior existence was likely in part due to the politics (i.e. American conservative allegations that Big Tech's pervasively censors right-wing and Republican voices).
It's a little strange, then, how Amazon took Parler's money until a day after others deplatformed Parler right after the election. Amazon's decision doesn't seem as arms-length and independent as you believe.