My nephew's wife is a TV producer. She has done a few of the international House Hunters. I asked her about the scripting. She says that they say what she tells them to say.
They need better producers. That said, it is an incredibly tired concept.
I agree, but it sells. If there was no market for this, it would go away.
Not just that it sells, but it is incredibly cheap to produce. No cost for talent, just a small crew to film for a couple days, some to edit, someone to do voiceover.
I'm just surprised they haven't squeezed in some product places... "honey, look at the beautiful GE select series stainless steel cook top! It accents the Lowe's installed granite countertops beautifully!"