I believe sometimes it’s done because there’s a lot to read and it might be (considered) too hard to read in real time. Which I understand, but it also annoys me too. It’s not what they said, and sometimes the way someone phrases something is important even if they don’t cut out important information, it can hint at their character or their emotion.
I don’t disagree that reading and writing are the basis of scholarship (as we know it), but I reject any suggestion that comprehending critical Marxist concepts should require a scholarly barrier of entry. If someone wants to become a theoretician then sure, it makes sense to analyse Marxist theory from primary sources with all its historical overhead, but if our goal is to promote efficient learning, then we shouldn’t be recommending archaic texts written for a whole different target audience. People don’t really need to learn French or German words to understand what the worker class and owner class are and their resulting material interests, or what alienation is. How many people need to know who exactly Kautsky was anymore? Can’t commodity fetishism be defined in simple terms? Archaic works absolutely still have value and relevance, but the Marxist ideas relevant to most workers can absolutely be made more accessible to your local audience while retaining its analytical value.