Production wants to shoot them as quickly as possible, as they are renting very expensive studio space and paying the talent for every shoot day.
Shark Tank is very efficient as far as TV shows go. Some shows, like Big Brother, shoot 100 minutes for every 1 minute aired. Shark Tank is probably closer to 3-5 minutes shot for every 1 minute aired. It's more like a scripted show in that regard. Certainly, all the pitches are memorized and practiced well in advance.
Someone asked my credentials. I worked on Shark Tank for one season as an editor. I have add'l credits on The Voice and Sarah Palin's Alaska for Mark Burnett Productions. I also worked for 10 other production companies on about 25-30 shows for ABC, NBC, CBS, FOX and SHOWTIME. Some of them I don't remember. Some of them I would like to forget, for example, Famous in 12: http://www.tmz.com/category/famous-in-12/