A large number of deported migrants are not running from any nation at all - many of them were raised from a young age in the country that will deport them once they become adults. They have known nowhere else; it is cruel and arguably immoral to send those somewhere else.

Some of them will be surprised, as they won't know they were from somewhere else.

Another large number are people from different countries who simply fell in love and want to be together in spite of law preventing them from doing so legally. It is cruel and arguably immoral to prevent them from being together.

A third large class are not breaking any law at all, it is the authorities breaking the law by not applying their own rules correctly or consistently. See also "deport first, appeal later" legal systems, where of course you can't really appeal once deported as it is impractical to do so.

A fourth class are people for whom the law is simply arcane and insane. For example people deported because one of their bank accounts dipped briefly below some threshold for a moment and there is an arcane rule saying it is not allowed. Or for not having long held a class of insurance that nobody knew about until one day people were being told to leave for not having it, and nobody can say how to obtain it anyway. Or for correcting a minor error caused by their accountant in their tax return, as encouraged by the authorities, and then being labelled a terrorist and threat to nations all over the world due to abusive misapplication of "bad character" law that wasn't created to be used that way.

And then there is the fact that nations of laws change their laws from time to time. Causing people who were once legally entitled to permanent residency to become unwelcome overnight.