the ICM model will over-estimate the value of a short stack on future hands. our 1k chips will also lose a lot of value because we will be hitting the blinds again in 2 hands (ICM does not take into account future hands). and next hand we shove into the BS with zero FE.
so we can take a negative edge (call with less equity than the ICM dictates with this specific scenario) because we should not treat this hand in a vacuum. we need to look at how bad our situation is next hand and the hand after that. and we discover that it gets worse and worse. so the ICM over-values our equity on future hands if we fold which means we call more.
pzhon has a video on the ICM model which explains this further