They do. It depends on what that instruction set is. If you have powerful operation codes built into those instructions you can do incredible things with a small amount of one for one assembled code.
A good example is the Spin Semi FV-1 DSP. It’s a stereo effects processor that is capable of some amazing sound processing. Check out all the free DSP code on their site to see how compact those programs can be.
The FV-1 happens to also be available as a submodule board from Electrosmith which also makes the Daisy that I posted about up-thread. Yves Usson used the FV-1 in his amazing effects box Les diffYUseur which i posted about over here.
So it depends on the hardware you run with your machine code, if all it does is load registers, perform simple math in registers, and write those registers to memory or device locations like most general purpose processors, forget it, you need a high level language and fabulous libraries (plus maybe an OS and task switching, and garbage collection, and …) to get anything done.
Also note the Ashun Sound Machine Hydrasynths are programmed completely in assembly code on their own custom built processors. It is likely done with the same sort of manner as in the FV-1 with each machine code instruction capable of directing a larger set of hardware parts each capable of running in parallel doing complex tasks.
BTW: All this programming is not done as exercises. 