Odium has had his eye on Dalinar for the past 30 years we think from reading his flash backs. Szeth is 34, maybe at about the same time, 30 years ago, she decided to cultivate a champion herself. Who better then someone who can train all 10 surges.
Timeline wise it’s all quite neat. 7 years ago Szeth is named truthless and forced to leave Shinovar, just in time to kill Gavilar 1 year later(and we all know what he was doing to help Odium).
Lift is young and Cultivation is said to be a Long term planner. Lift is going to be big in the back half for sure. But I think it an interesting twist is Szeth was a big part of cultivation’s plan in these first 5 books and I think it fits.