I'd bet there's a correlation with the difficulty one plays the base game at. People who're comfortable playing Insanity probably also prefer Gold MP. Me, I've never played SP at higher than normal (and that was enough), so yeah - Bronze is about my speed. I've tried Silver a handful of times, but only won once. Never even considered getting instantly slaughtered by Gold.

I started out on Normal and in fact first tried hardcoe and Insanity in ME3. With a little practice I became good with it and with a Geth Engineer and Geth Plasma Shotgun and exploiting the ridiculously stupid AI getting "instantly slaughtered by Gold" has never been a problem for me, unless one teammate leaves.
What am I missing about whats wrong with bronze?
I generally only play on bronze because if I'm playing multiplayer it's purely to boost my readiness. I bet that's the case for most people doing it too.

Maybe Bioware should have included an option for those playing just to enhance their SP options.

I think Bronze is a waste of time since a Bronze match lasts about 15 minutes and nets you around 10,000 gold. A silver match takes about 16-20 minutes and nets you 30,000 credits. Gold fights take 25-30 minutes and reward you 70-80,000 credits.
Thus, it's vastly more cost effective to play either Silver or Gold.
Personally I play only Gold since through sheer training I've become pretty good at it that, without bragging too much, I can stem the tide enough for any crappy team to make it through. And of course I pick my teams carefully.
What do you think of this "Rebellion" DLC rumors?
I will likely not touch it before the Extended Cut unless it proves to be genuinely good.