There are a few obvious reasons: size vs price being the most prominent of them. Direct view televisions increase in price by multiples in sizes over 70” diagonal with prices doubling from 70” to 80” and doubling again from 80” to 90”.
Whereas an entry-level 90” direct view television currently retails for > $7,000.00, one can put together a projection based system of the same image size and performance for well under $1000.00 including, projector, screen surface and basic, “at least as good as the direct view television”, sound system. It's worth considering as well that your 90” direct view television represents almost 25 square feet of plastic and metal occupying prime visual real estate in your home even (especially!) when it's not in use.
Why Does Size Matter?
The more of our field of vision that is occupied by an image, the easier it is to suspend disbelief and become engaged with the content being presented. Whether that content is a film, a videogame or a sporting event, ideally the screen will be large enough so that, from our viewing position, it will be impossible to keep the entire image in focus at the same time. In other words, we want the image to be large enough that we have to move our eyes to keep to be able to focus on the far left and right of the screen. Why you may ask?
Let's Get Physical!
As soon as we have to start moving our eyes, our attention is engaged in a physically different way than when we can gather all relevant information in an image at a glance. When we have to focus on the right side of the screen, we don't know what is happening on the left. This uncertainty is what prompts a classic flight or flight response physiologically in us: elevated heart rate, elevated adrenaline levels and heightened awareness. Sounds like a recipe for a perfect entertainment experience to us!