Why would some company or network sponsor a grand illusion?

To Make Money.

The US Corporate Trade Show market is a good example. Companies need to look different. Some will spend big bucks on magicians to get their point across. Hence, they "sponsor" big illusions.

It is more of a "head" turner ... if you are looking at a magic show that is sponsored by Kraft, you won't be looking at the competition.

DC was sponsored by Kraft for a long time.

Same with trade shows on a smaller scale. If you are standing in front of or lured into xyz's booth you aren't going to spend your money in someone else's therefore increasing xyz's chances of making a sale.

They may be willing to pay you to do just that...