Why encirclement did not make Ukrainian surrender automatic

Why would encircled Ukrainian forces continue fighting instead of surrendering?

Because control of prepared urban terrain could let them inflict heavy losses and wear down the attackers despite encirclement.

The question cites claims that surrounded Ukrainian formations should already have surrendered. Encirclement alone does not prove that a defended city or force has become untenable. Troops controlling an urban environment can compel the attacker to enter streets and buildings, where the defender's positions and local knowledge impose heavy costs. In this contemporary reading, the Ukrainian purpose was to wear down Russian forces even when the wider operational position looked severe. The comparison with how Americans or Britons might react to an invaded home city exposes the assumption that surrounded defenders lack a political reason to continue. This is a March 2022 assessment rather than a later reconstruction of the battles.