Who are these people who want to own a thistle, yet alone pay for one?

Cultural and aesthetical reasons. Same as cacti.

There is a category in landscaping for plants that are strongly geometrical, tall and bold. They are called architectural plants and are a important design element to provide interest out seasons. A good design takes care of color and tone but also will include texture and tactile appealing. Some thistles are native, undemanding and can be really beautiful in winter covered in ice. They have often interesting patterns in leaves and flowers. The indigo flowers of the artichoke in top of a silvery foliage are really spectacular.

And thistles attract lots of interesting insects.

The problem is not that they are thistles, is that they aren't native and in this case also poisonous.