Humans are irrational beings and when you realise up to 60% of these women end up in a shallow grave or a lake held down by rocks you'll understand why they're too scared to leave.
Especially women of lower socioeconomic status. Richer and well off women have plentiful venues to seek help. Amanda is literally penniless and isolated by a fat abuser. If she dares to try and leave, she'll be met with violence which I guess would be fine in her mind, how about Rozy? If Ethan Ralph is happy to weaponise cozy.tv Rozy against Harry, then he's surely capable in doing the same against Amanda. Amanda has a history of paedophilic inclinations, Gunt will use that to try and gain full custody of cozy.tv Rozy.
That's also why Harry is still willing to accept Amanda. She's such a fuck up, why not cut loose? Logic fails in both cases.
Faith was the lucky 40% and she was in America, foreign land but not a foreign nation. Ethan Ralph learned from this, that's why he's in Mexico. Honestly, Amanda's best bet is to get Ethan Ralph drunk, or even spike his cheap booze with sleeping pills and then make an escape. Get to some safer place in Mexico full of expats and the get a hold of Harry.