Even though your MBP, and many others, still has rotating rust media, Apple is always building for the next generation of devices it is reasonable for them to remove features from the OS that are dangerous or ill advised in the current and future hardware generations.
I'd have guessed that OS X/macOS would treat secure erase similarly to the way (as we recently discussed in another thread) it's treated disc drives and trackpads, i.e. intuitively, wherein it knows what you're running and gives you the applicable options.
