Short answer would be historical reasons. https://en.wikipedia.org/wiki/Unix_filesystem https://en.wikipedia.org/wiki/Unix_filesystem "Contains locally instal

Short answer would be historical reasons. https://en.wikipedia.org/wiki/Unix_filesystem https://en.wikipedia.org/wiki/Unix_filesystem "Contains locally installed software. Originated in System V, which has a package manager that installs software to this directory (one subdirectory per package)." Solaris made extensive use of /opt, that flowed into some Linux packagers. It then fell out of favor as everyone put everything in /usr