I think it's the combination of soft, soft furry fur and that purr. That purr is nearly deadly, it's so weakening.
If dogs could purr, they would be in a much better position. But on second thought, it wouldn't work for them; they are such pushovers for affection that they would be purring all the time. With cats, it's an unexpected reward after a day of being actively ignored and barely despised.
My arm hurts from holding my elbow up to keep from smushing Coco who is insisting on viewing my typing from my lap.
Yes, I could shoo the cat away. But I won't.