Why Soviet industry struggled with very thick armor

Why could Soviet industry not readily produce the very thick cemented armor required for its capital ships?

Knowledge, tooling, and resources all constrained production, while reliance on German imports exposed the program to slow and delayed deliveries.

The difficulty was not caused by one isolated technical defect. Metallurgical knowledge, industrial tooling, and available resources all imposed limits. Soviet planners therefore sought armor and related warship equipment from Germany. German suppliers moved slowly on the promised material, demonstrating how a domestic industrial shortfall could become a strategic schedule risk when foreign supply was uncertain. Allied firms could probably have sold armor without receiving special access to Soviet yards, since convoy warships already gave Soviet observers opportunities to see those facilities.