There is a practical, empirical distinction between compilers and transpilers. Most compilers in practice have backends full of deep and well-explored techniques specific to machine code like register allocation, window optimizations, and other stuff like that. Most transpilers you see out in the wild share more in common with compiler frontends in the techniques and the theory they apply.

The term transpiler arose when there was a need to denote a special kind of compiler whose target is another language or version of the same language.