I disagree with it, but the premise is that they cant be upgraded so they are stuck at a set spec, they struggle with heating and dust issues, they make a lot of sacrifices due to needing to fit into a laptop size, and they basically need to be plugged in 24/7 which bites at the portability.
All valid points, but also all acceptable trade offs if you need a portable and flexible machine.
Upgrading or cleaning a laptop means opening up the laptop. Anyone who has opened a tower and a laptop will attest, the laptop is a nightmare to deal with and the tower is much simpler.