In the Linux FHS, it says all third party packages should use /opt. However, I didn't see anybody is using /opt. Also, /opt is not in $PATH in anyway, so I think the OS is not intended to let us use /opt. So why bother to create /opt there since nobody is going to use it anyway.
You guys might think this is a duplicate, but clearly it's not. I know about the difference and the thread, but I just don't know why nobody is using it.