The sibling comment correctly explains why the article doesn't say what you thought it did, that the US had been giving aid to Ukraine since 2014 and only in 2018 specified that none of that aid should go to a particular militia.

The real reason the US didn't arm Ukraine was that it didn't want to provoke Putin into escalating the conflict: https://www.latimes.com/world/europe/la-fg-ukraine-russia-we...