http://www.dandwiki.com/wiki/SRD:Frightened
A frightened creature flees from the source of its fear as best it can.
If unable to flee, it may fight. A frightened creature takes a
–2 penalty on all attack rolls,
saving throws,
skill checks, and
ability checks.
You can't flee in PoE so actually it made sense.
So many arbitrary mechanics to deal with an issue strategy games have solved a long time ago: giving characters Morale and allowing them to flee.
Brave, disciplined, and loyal characters have high Morale. Characters with the opposite personal qualities have low Morale. Morale decreases automatically as the character takes damage and becomes fatigued, or is hit by Morale reducing abilities like Fear.
As Morale decreases, there is more chance for the character to flee or skip its turn.
You can increase Morale by healing characters, inspiring them, and defeating enemies. Certain systems also give combat bonuses for high Morale and penalties for low Morale.
This is 2018, characters not being able to flee from battle is just ridiculous.