Marx avoided theorizing finance because of his insistence, not its unimportance.

Evidence

The reason Marx never developed a full analysis of finance is not because, in his day, it was a less important force than in our own. Indeed, Marx’s career was witness to many bank failures and financial crises, as well as to the tremendous power of the financial sub-class over state policy. His reluctance to address the financial sector in detail stemmed, instead, from his insistence that any understanding of it would need to be grounded in the analysis of capitalist exploitation more elementally: the extraction of surplus value from workers (the subject of volume I) and the processes by which capital reproduced itself in circulation (volume II). — Max Haiven, Cultures of Financialization, 97

Categorization

• QUESTION: The sentence cuts off at ‘his insistence that’ — the actual reason is truncated in this excerpt. Worth chasing what exactly Marx insisted that precluded a full finance analysis.
• XREF: connects to: Marx and Weber avoided theorizing imagination because they rejected Romantic liberalism — Aris Komporozos-Athanasiou, Speculative Communities: Living with…, 229