99% of the time, Materialism means being driven by greed(material wealth), while idealism means being driven by moral principles(ideals). This set of definitions is NOT the one that philosophers used.
Marx and Engels discussed materialism and idealism in philosophy, which is a completely different thing. Even in philosophy, both terms are extremely vague and are not enough to mean anything on their own without pages upon pages of elaboration.
It's laughable how online leftists throw around these words without even knowing what they mean. No, calling something "idealist" is not a valid critique and saying "material conditions" instead of "reality" does not make your argument stronger. Read an actual book for once and never ever use those words again. Save them for serious writing of substance.
99% of western leftists are idealists. I learned about communism as a teen from my cousin who was in the CPRF Komsomol at the time, and had a thorough education of dialectical materialism. I was 25 by the first time I encountered someone claiming to be a "materialist", and all of really meant was that they were against liberal identity politics. I can sympathize with that, but the more I talked to these people the more I realized they were basically just a different flavor of liberal (Stupidpol folks).
The grim reality is that the only materialist leftists in the west have realized that material conditions aren't anywhere near the point where revolutionary potential is recognizable and have thus given up and sunk into their personal lives for an attempt at happiness, or at the very least an escape from misery.
bullshit