Well for one thing FF Meta isn't free or Free and is probably also trademarked.
Having an OFL (Open Font License) font of high quality is a good thing.
Also OFL licensed is Andika (http://scripts.sil.org/andika) which I'm using in an app for children as the letters are mostly in the form that they would be handwritten was the best I could find in a few hours searching (free and paid) and most of the licenses for use in apps looked very expensive.
I agree, licensing seems the most plausible reason for releasing it under a different name.
Also, I like Andika. To me, it looks like a proportional-width interpretation of Monaco, a monospaced font that has shipped with Macs for the last few decades.
Those look pretty different to me. I mean, very clearly related, but with tons of small changes. Like, the angle of almost every terminal is different, and in general the new typeface is much more vertical.
Yes, as someone said below, what's the difference between most programming languages? Very small changes in the grand scheme of things, they mostly all have variables, classes, functions, etc. It's the same thing with fonts, they mostly all have the same sort of form, with variations. Put that font beside Arial and Helvetica and you can probably see similarities between them as well, yet they have a different name.
Arial should have never come to be. The only reason it exists is because changing it a little and giving it a new name meant Monotype didn’t have to pay Linotype license fees.
Arial was originally it's own font (Monotype Grotesque), but got squished to match Helvetica's metrics which is a good example of how fonts can be different and similar to each other.
As you can see, all the areas in which Monotype Arial is different from Linotype Helvetica are borrowed from Monotype Grot. The reason to make such a monster is purely financial.
I made a quick side by side comparison between Fira and Meta Pro: http://i.imgur.com/Oo3yeYx.png