As I browse through the various sites and booking engines I do see breakfast slowly becoming optional. I guess the term B&B will just have to be B in the future if the trend continues. I especially notice it for places near airports.
I suppose it is one way of increasing prices without seeming to. Make breakfast an extra. Like downsizing the weight of a package but charging the same price = actually increase in price.
I noticed it when I started seeing B&Bs listing on Booking.com and hotels.com... a lot of people shop by price on those sites and might not notice the "extra" -- so B&Bs were matching the hotels.
On the otherhand, a lot of AirBnB hosts are offering a lot of extras like breakfast or a stocked pantry -- hosts are obsessed with their reviews (it's the only way to succeed in the AirBnB ecosystem).