It saves them money and, lets face it, it's unlikely that you will ever wear that gown again. After all, those pictures will last a lifetime. If you don't have a great photographer, you're not going to get great pictures. So you don't really want to skimp too much there. That wedding album is something you will keep out on your coffee table for a long time and guests from your wedding will want to see those pictures of you and them.
Locations can have a wide variety of costs, ranging from free into the thousands.
You need to balance this out also because saving money by having it outdoors at a park could also mean losing guests early on because of the weather and temperature. Finally, we come to entertainment. If you don't have any entertainment, then most of your guests will leave right after they eat. Conversely, if you didn't have any food, but still had entertainment, most would probably stay for a while. They will also be happy with just about any decent meal, which is why so much chicken is served at weddings.