Amelia Lacoste was guaranteed a spot because she is WS20. Imai was guaranteed a spot because she was WS21. Miyahara was guaranteed one because she was Top 24 SB, and, in addition, she got a discretionary host pick, which is standard when a host wants to give their top junior-turning-senior good opportunities. The selection rules don't care whether or not we have a problem with their selections.
Neither Zhang nor Cesario is guaranteed a spot, making the Skate America appointment the topic being debated. Cesario placed higher than Zhang at US Nats, and her SB, earned at a junior competition, was 7+ points higher than Zhang's at last year's Skate America. Cesario is also 12 places higher than Zhang on the SB list, which should mean Cesario should have a good chance to be an early pick as an alternate, but based on last year's experience, this is a gamble. Plus Cesario can still be appointed to the SA TBA spot, which generally happens around Labor/Labour Day.