The female demographic that currently consumes Tales likes romance with male and female characters, they just don't like how Tales of series normally writes romance. And their attitude to romance is that "if you're not going to do it well then don't do it at all".
Basically, if there's going to be romance then make it blatant and make sure that the Male and female characters have a lot of chemistry. None of that "te he, we haven't even held hands yet", but an actual romance.
In fact the relationship between Emil and Marta is preferred by them and would be more popular if Emil wasn't so thirsty for Richter.