Arch still occasionally has some packages installed to /opt. Annoying as hell, but they expect to be there for some reason. Android-studio was the latest unexpected surprise for me.
I've seen distros choose /opt for software not built by the maintainers, but simply repackaged in binary form. This would include software like oracle/sun java.
Once upon a time, I read the LSB[1] filesystem hierarchy, of which the only thing I consider useful was that non-distro-provided third party software (i.e. anything you'd buy on a disk and install) should live in opt. It didn't make a huge deal of sense then and it still doesn't now, but it sorta provides a way to know which directories can safely be rm -rf'd.