Why not flavor with malts? I haven't looked into the history of American beer, but many styles seem to come from the price of local ingredients and qualities of local water. That makes me things hops were cheap and plentiful and caused the IPA trend.

I'm not a super expert, this is just what my friends in the biz have told me. I wouldn't be surprised if several factors conspired to create the IPA trend. Yes, there are many ways to infuse flavor into beer, some of which you mentioned above. My friends make IPA styles, but also many others using all kinds of tricks like malts, waters with different minerals, pHs, different base ingredients, brewing wheat in different ways. My buddy even domesticated a new strain of yeast.

If you're in Boston, give Aeronaut Brewery in Somerville a try (https://goo.gl/maps/bm22XaBvFPQ2). I have something of an interest of it, but I (unsurprisingly) recommend them.

Aeronaut is a great option for some new flavors. They do all-out hoppy IPAs, but if that's not your thing the other options are distinctive and tasty.

Hoppiness is partly a reaction to the variance in hops and a pride in "American beer". Cascade hops in particular are cheap, available, and have a strong and distinctive flavor; hence the popularity of IPAs on the west coast, and the presence of companies like Sierra Nevada in the hoppy vanguard.

Even as the Cascade trend has diminished, lots of people have 'reacted' by rediscovering other hop flavors and advertising things like Nobel hopped beers.

Having said that, it's all getting a bit played out (except on the west coast, perhaps) and I'm starting to see more experimentation with other stylings like wheat, fruit tones, and dark ales.

I have wondered about the same thing--both hoppiness and maltiness are good reactions against bland mass market beers, but somehow big malts never took off the way hoppy IPAs did. Is it difficult/expensive to make malty beers?