Busybox’s directory structure (bin, sbin, usr/bin, usr/sbin) originates from 1970s Unix, where space limitations led to the /usr mount for user files. The split lacks relevancy today due to modern boot processes, shared libraries, and larger storage capacities. Over time, bureaucratic rules developed to justify the structure, but current practice is often arbitrary. Developers like Rob Landley simplify their systems by linking directories for practicality.
https://lists.busybox.net/pipermail/busybox/2010-December/074114.html