"Room and board" is valid compensation in some jobs. There are valid jobs to this day where having a place to stay is a large part of the compensation you will receive.

It is not as black and white as you seem to think.

To put some clearer relief around the point: the author's parents had no means of keeping Lola in their home by force. They had no right to shoot or maim her if she attempted to leave, and would have been convicted of murder if they did. But where would she go and what would she do, illiterate, with no education or practical experience with worldly matters, no skills, and uncertain legal status?

Few human beings will cope with that level of uncertainty, and to imagine that they ought to is, I would say, a conceit of someone who is unable to properly situate themselves in that person's shoes as a mental exercise. The familiar, with all of its unpleasantness, can be a welcome refuge from the fear and uncertainty of the outside world, especially if the familiar is all you know, you have few bases for comparison, and weren't brought up socially to embrace fear or uncertainty to any degree.