That's not entirely true, not everything is garbage collected. With some care, you can get a whole lots of things allocated on the stack. Tooling can also help you figure if things escape to the heap.

You can also control the size and number of objects your program creates, which impacts the performance of GC. Sure you can't pick a GC from a stack of GCs, but you do have many things in your hand to control how memory will behave.