Practicality, is the keyword.
Nobody goes out to purchase a super-duper-HD-TV, just so they can have the sent signals upconverted to higher definition. Makes no sense to spend the extra dough that it would cost just for that.
You don’t get out much, do you?
If it gives a smoother picture on a very large screen than an unconverted signal does, people will buy it.
I had a very high quality up-converting DVD player that made standard def videos look damn near as good as high def, and hung on to it for several years before they settled on BR as the standard for high def video.
Worked for me.