It also does that for, basically, one device (the three models available so far are almost identical. Fan/no fan, and some binning on the GPU)
That’s one further reason their system is faster: they designed a system, and the design of their CPU, GPU, etc. was driven by what the final system needed.
Other system manufacturers buy individual parts, where the manufacturer of each part extends/optimizes it with only a vague knowledge of what the system it will be used in will look like (and they don’t want to focus on one specific system, as that would mean they can sell it to fewer device manufacturers)