Hi there,
I don't have a therapy dog, but the nursing home my great grandpa stayed at employed several. He loved them! I honestly think he loved the people that brought the dogs as much as the dogs

What I enjoyed most was seeing him make efforts to engage with the dogs and the humans with the dog. The visits drew him out of monotony. For my ggrandpa, I think the therapy dogs were a comfortable(warm and fuzzy), safe, sometimes nostalgic way to connect to his deteriorating mind.
I'm no expert, but those are my thoughts!