Two reasons:
1) They have seriously good quality control.
2) They're made in the U.S.A.
Of course, you can visit the EBMM Forums. Here's the thing -
(1) Mr. Sterling Ball has a commitment to his employess to provide a 'living wage,' which means he pays decent wages (in SLO, coastal California!) to his workforce. (Strings are made out in Indio, CA - middle of the desert).
(2) Their QC is really amazing. Unlike "many competing brands," you don't have to try 3 or 4 or more - just order the specs you want or pick it off the wall. I have two "Balls," one off the wall and one special order. Both were perfect.
(3) They don't produce at huge volumes. It's not a huge company. You can call/email customer service and they answer right away.
(4) They invest in music (Warped/Battle of the Bands Tour, etc., etc...) and musicians.
(5) They're innovative. Even if you don't like the Bongo, that was a concerted investment & design effort.
(6) They're REPAIRABLE. And they service what they sell, just like Mercedes.
Personally I don't think $1300-$1600 for a US built, well made and well designed instrument is a lot of $. That might seem like a lot of money if you're young and starting out, but if I were playing professionally, I wouldn't consider my primary tool-of-the-trade overpriced. If I'm depending on the tool to work every time, I don't want to go too cheap. (Old joke was the two soldiers in the foxhole, reminding themselves that their weapons were made by the lowest bidder..)
There is a thread from last .. February? March? someplace..in the EBMM Forums where Sterling himself agonized over revitalizing a low-end line, like OLP, which were made overseas. (I believe they're relaunched OLP). He wants to have an affordable, entry level instrument, but the challenges are supervision of the overseas effort, brand dillution and of course, QC. Fender (and I own one) confuses the heck out of me with MIM, MIJ, MIA, Squier, Fender, etc., etc.
My $.02. I think EBMM is a great company, producing a great product. Even if you don't like the "MM Tone," I think most would agree that they are a very good "value for dollar paid."