In an Islamic court if a girl during Nikkah isn’t given the husbands right of divorce and she applies for Khula then she has to give the meher back. If she has spent it then who knows. Legally hard to take from someone what they don’t have. Then again I don’t know anyone who pays a huge amount anyway.
People either write huge amounts to show off to their family, and some girls write less to show how noble and trusting they are. Cultural things again !