The structural challenge of multiple timelines
Multi-generational fiction makes structural demands that single-timeline novels do not face: multiple sets of characters must be established and maintained, multiple historical periods must be rendered with sufficient specificity to feel real, and the connections between timelines must be clear enough to orient the reader without being so explicit that they feel mechanical. The structure that works is the one in which each timeline is genuinely necessary — not just context for another timeline, but a story worth reading for its own sake that also illuminates the timelines around it. The writer who loves one generation more than the others will tend to produce a novel in which that generation's timeline is fully realized and the others are underdeveloped, which is a structural imbalance that readers feel as unevenness of investment.