The Moto X is the only phone that matters because it's not a Droid and not basically tied to Verizon like the Droid Ultra/MAXX/Mini happen to be.
Just sheer economics at work: the Moto X is available from multiple carriers and is more popular because of that fact, so it will obviously make more money for companies that create accessories for that phone.
Hell, I went into a Verizon store the other day looking for a screen protector for my Mini - that's Verizon, the company that sells the damned phone in the first place - and they were like "We don't have any accessories for the Mini..." and they didn't. Not one thing for the Mini at all, which is pretty damned messed up in my opinion.
I don't know what kind of contract Verizon made long ago with Motorola for the Droid lineup, but I sure as hell wish it would come to an end soon.
Currently using nothing at all...