Did you notice TV has been gradually falling in the vote rankings?
They were #1 the first week, #2 the week after, and #3 this week. Will it be #4 next week?
And it's not like much has changed about their singing since then and now.
I suppose in the beginning, they were just the perfect good-looking couple who people voted for at first look. But now, having seen others perform as well, poeple have also begun to like others and started voting for them instead. Hence TV support is waning.