I'm starting to wonder if it's even worth writing about phone makers other than Apple and Samsung.

Apple and Samsung between them now own 87 percent of postpaid sales at the big four national U.S. carriers, according to new stats from principal analyst Cliff Maldonado at mobile-focused research firm BayStreet Research.

Everybody else is fighting for 13 percent of that market. Motorola, ZTE, Huawei, Sony, LG, BlackBerry, HTC, Microsoft, Alcatel, Sharp, Nextbit, whoever—they're all scrabbling for 13 percent of the postpaid market, the highest-spending segment of the U.S. mobile market.

The situation is slightly better in prepaid, which includes the carriers' sub-brands like MetroPCS, Cricket, Virgin, and Boost, as well as the 25 million-strong TracFone brands. There, Apple and Samsung represent 71 percent of sales, and the dozen other brands in the market duke it out for 29 percent. But even though prepaid is seeing all sorts of new entrants like OnePlus, Blu, Oppo, and everyone I list above, the top two makers' dominance is increasing, especially as Apple's older devices filter down to prepaid customers.

This is completely different than what we're seeing globally, where Huawei and ZTE are booming, according to Neil Shah of Counterpoint Research. An array of "other" manufacturers plays a much larger role outside the U.S. than here, according to data from Ben Bajarin of Creative Strategies.

Looking at Bajarin's global data, you find that global smartphone competition has been heating up. Local Chinese and Indian manufacturers, especially, have been cutting into Samsung's sales in those countries, with companies like Xiaomi and Micromax shooting to prominence in the past few years. Companies don't need to have a U.S. presence to survive, or to thrive.

The diversification of mobile manufacturers simply hasn't been happening here. The two massive leaders have just been tightening their grip. In our reviews, we pretend that Americans can and would make great choices like picking the Moto X Pure Edition or Huawei's Nexus 6P over the dominant models. But while those phones' fans are vocal on the Internet, they're just not shifting enough sales to move the needle.

When Will It Change?
Duopolies are bad because they get lazy. Vibrant, competitive markets tend to be better for innovation, and there are enough different kinds of people with different needs in the U.S. that, at least in my view, they should have different choices available.

The reasons for the duopoly aren't entirely obvious any more. It's difficult to break into the U.S. because Sprint and Verizon require CDMA radios, but Motorola, ZTE, LG, BlackBerry, and Microsoft have had no problem with that requirement. You could blame the fact that 92-95 percent of our postpaid phones are sold through carrier stores with financing plans, which definitely makes it harder for new entrants like OnePlus, Oppo, and Blu to make a big splash at retail with high up-front prices. But that doesn't explain why Motorola, Sony, HTC, LG, and Microsoft, all of which have long, well-established carrier relationships, are going nowhere. Samsung does a lot of marketing, sure, but so do LG and HTC.

Execs at ZTE and Huawei, the two booming Chinese manufacturers, say that our market will flip over to being largely unlocked phones sold outside carrier auspices within the next two years. HTC has shown with the HTC One A9 that it's possible to make a Verizon-compatible phone without expensive CDMA testing and verification. Microsoft has opened 85 stores to try to fight Apple's first-party retail dominance.

Those are all moves that could bring competition back to the smartphone market. Something certainly needs to change. While Apple and Samsung both make good phones, they're not the only ones who do.