Many girls ARE in effect “hostage” when they are waiting a long time for a response from the boy’s side. I know so many girls who strongly (and in my opinion wrongly) hold that it is wrong to make a date with someone who is ready to say yes, if the girl is still waiting to hear from someone else who was suggested before this, but who just did not get back to the shadchan yet (maybe because he has “lists” of girls). IMHO it is stupid and a waste of precious time, to fail to agree to meet someone else, just because the person you are trying to meet is taking his time (or whatever reason is holding up the works).
I know someone who missed out on a potentially great shidduch (yeah, yeah, if it were truly bashert, it would have happened anyway…blah, blah blah), because it was suggested while she was still waiting for a response on another shidduch. The other guy finally got back to her shadchan, the date unfortunately did not go well, and by the time she agreed to talk about the other boy (who would have gone out with her had she said yes instead of waiting for the first guy), he was busy with someone else, whom he eventually married.