The "need" was to try to get the US govt (and others) to support the antifascist cause abroad.
Let's please remember that the CP wasn't a local revolutionary groupuscule, it considered itself a battalion of a worldwide army HQ'ed in Moscow.
SA
^^^^^^^ CB: The international connectivity of the CPUSA was not a shortcoming of it, but a Communist plus. Recall that Marx and Engels founded The _Inter_national. Marxism is proletarian internationalism. The CP , by its fundamental principle was supposed be part of an International. CP in the Marxist tradition aren't supposed to form local national groups. Kind of made sense to coordinate it in Moscow since there had been a Communist revolution there.
As far as "battalion" , "army" etc. if you think there wasn't an international class war going on both literally and figuratively, then you are very mistaken.