He believed such a flight would indicate a fear of death, which he believed no true philosopher has.
If he fled Athens his teaching would fare no better in another
country, as he would continue questioning all he met and undoubtedly
incur their displeasure.
Having knowingly agreed to live under the city's laws, he implicitly
subjected himself to the possibility of being accused of crimes by its
citizens and judged guilty by its jury. To do otherwise would have
caused him to break his social with the state, and so harm the state, an unprincipled act.
If he escaped at the instigation of his friends, then his friends would become liable in law.