Fame
Though there are a great many famous mechanical engineers of Yore, there haven't really been many who've risen to the coveted status of "household name." Sure, you've got your Nikola Teslas, your Kitaw Ejigus, and your Kumar Bhattacharyyas, but they got famous many years ago (source).
You know, when less stuff already existed. Where's the star mechanical engineer for the millennial generation? It could very well be you.
Unfortunately even most of the stars in this field never make the headlines. Innovation happens at such a fast pace now that it's pretty hard to credit someone with a breakthrough when yet another engineer builds upon that work with something equally groundbreaking. Info is so readily passed around and collaboration so integral to today's pace of workflow, it's more likely for teams of engineers to get praise rather than a single, solitary innovator.
Your best bet? Build something cool (and maybe kind of dumb) like a robot that composes music. You'll probably get your own reality show.