Arranged marriage is not same as in past. Families have become more hypergamous too.

[robtical]

In past, people were a lot more closer socioeconomic wise and people did not run into higher socioeconomic in general. Unless through servitude jobs. Now, you have access. The families also are more picky, aka middle class want groom from higher class. Higher class want from fellow higher class, etc. Kinda like short girls going for tall guys, tall girls going to tall guys.

Sure it can happen that low socioeconomic girl arranged to low socioeconomic groom. But these arrange marriage happen because the families were good friends and want to change their friendship into relation. So in theory, lower socioeconomic family want higher socioeconomic family than them. They would rather feed and raise their daughter to death than marry her off. Exceptions are trying to get rid of girl as she is liability on finances.