That extra nonsense is generating revenue to the manufacturer of the product

At this point we might as well cut out the middleman and pay people to connect a black box to all their devices.

In the case of TVs I think it also has to do with there being no real hardware difference between a fancy Smart TV and a dumb TV. A dumb TV nowadays is going to be implemented as essentially a computer and monitor running a set of TV applications, just like a Smart TV. The only difference will be that fewer programs will be loaded onto the dumb TV.