The problem is the hard limits of physics. We have an upper bound for the number of interacting elements required for intelligence in the form of number of synapses in the human brain. That number is a thousand trillion. We don't know what the lower bound is. Neurons are ferociously efficient computing devices, though. A dragonfly can take input from thousands of ommatidia and use it to track prey in three dimensions using only sixteen neurons. How many transistors do you need to do that? Let's be generous and say only ten percent of the human brain is needed for sapience, or 8.6 billion neurons. 8.6 billion / 16 roughly equals five hundred million. Multiply your earlier transistor number by five hundred million. There's your lower bound for a sapient computer.

There is no law of the universe that says it has to be possible to generate human-level sapience with less than one kilogram of processing mass. In all likelihood we are never going to create a server with a whole city of intelligences in it, ever.