Many students who have intentions to do 3-2, end up not wanting to leave their friends at their LAC the year before graduation there. They end up w no engineering degree,
Those who do transfer end up paying for AT LEAST an extra year (5 years total), if not 2 extra years (6 years total) because they have a hard time scheduling the requisite courses within that period,
Then there’s the pesky issue that you need to apply and be admitted into Columbia or other school. Admission is not guaranteed.