Space and time saving measure. Instead of hundreds of programs you have one "box", which can do it all. Program names are the same but they all point to this box. The box reads the original command line and acts accordingly. If the line starts with "cat" it acts like a cat. If it starts with "cut" it acts like a cut.

Small footprint basic system utils, good for constrained systems and early boot, basically. Where utilities themselves are very small, it avoids executable 'boilerplate' that would take up space.

Custom embedded Linux systems without GPL code in user space.