Layman understanding:

Because as a function of hardware and electricity costs, a “cloud” GPU will be many times more efficient per output token. You aren’t loading/offloading models and don’t have any parts of the GPU waiting for input. Everything is fully saturated always.

I believe GP means it still to be connected to 'if this kind of latency is unacceptable to you' - i.e. you can't load/use/unload, you have to keep it in RAM all the time.

In that case it's massively increasing your memory requirement not just to the peak the model needs, but to + whatever the other biggest use might be that'll be inherently concurrent with it.