Consider the biggest store in your city that sells home appliances including vacuum cleaners. Clearly this store has a lot of reach because many people know about this store. You can go and buy a vacuum cleaner from there. However, almost certainly you are not going to get a lot of detailed information about the vacuum cleaner you are buying because the salesman there sells many other brand names and can even be a salesman for other types of appliances. On the other hand, think of the salesman that comes to your house and wants to sell you a certain type of a vacuum cleaner. Obviously, he would answer all of your questions about the vacuum cleaner and will give you lots of additional information about it. Clearly the information you get from him is very rich, however its reach is low.
Assume you want to make some advertisements about a certain product. You can rent a billboard and hang a sign on it containing the name of that product and perhaps a photo of it. The reach of the billboard is very big because many people will see the sign but its richness is low because you can’t write a lot of information on the sign. You can however write a detailed brochure about the product. The brochure will have less reach but more richness of information.