That's just not true. To give you a few pieces of the picture, moving collectors move little memory and do so rarely (relative to the allocation rate):

In the young generation, few objects survive and so few are moved (the very few that survive longer are moved into the old gen); in the old generation, most objects survive, but the allocation rate is so low that moving them is rare (although the memory management technique in the old gen doesn't matter as much precisely because the allocation rate is so low, so whether you want a moving algorithm or not in the old gen is less about speed and more about other concerns).

On top of that, the general principle of moving collectors (and why in theory they're cheaper than stack allocation) is that the cost of the overall work of moving memory is roughly constant for a specific workload, but its frequency can be made as low as you want by using more RAM.

The reason moving collectors are used in the first place is to reduce the high overhead of malloc/free allocators.

Anyway, the general point I was making above is that a machine is exhausted not when both CPU and RAM are exhausted, but when one of them is. Efficient hardware utilisation is when the program strikes some good balance between them. There's not much point to reducing RAM footprint when CPU utilisation is high or reducing CPU consumption when RAM consumption is high. Using much of one and little of the other is wasteful when you can reduce the higher one by increasing the other. Moving collectors give you a convenient knob to do that: if a program consumes a lot of CPU and little RAM, you can increase the heap and turn some RAM into CPU and vice versa.