Unfortunately, sometimes ads do not get seen by the right people. But that does not mean that the right people are not out there.
Don't take this as criticism, but maybe "serious cat - loving person" was not quite the right wording. My friend Lisa is a serious cat loving person, but she would not do well with a shy type of cat. ( and not all rescue cats are shy ). You might need to just word the ad differently. Or try different locations to advertise.
While the cats would do well (VERY well) if they stayed with you, it may not come to that.
Try not to give up all hope.