The world is very small, and it can't support that many companies making passenger aircraft. If you want aircraft of that size, you have to buy Boeing or Airbus. Both are sold out until the 2030s.
There's an apparent contradiction here.
China spent ~15 years developing the C919, and it's finally entering mass production. But it also appears to be sold out until the 2030s.
While there is a growing demand for passenger aircraft, the fixed costs of getting into the business are so high that the market cannot support that many manufacturers. Not on a commercial basis, anyway.
Airbus and Boeing are commercially viable, and they have customers all around the world. Comac is more of a political project, as China tries to reduce their dependence on Western technology. There are 1000+ orders for the C919, but effectively all of them are Chinese.
Similarly, the USSR had domestic passenger aircraft industry, and Russia retains some capability to manufacture them. Their latest model is the Irkut MC-21, which has a few hundred orders. Again, effectively all of the orders are Russian.
Then there is Embraer, which is the biggest manufacturer of regional jets. They have been decades in the business, but they have not made any attempt to build a competitor for the A320 and B737.
In fact, their first product, the A300, was a technological milestone, and sold 561 after initial difficulties. The A310 had more industry firsts. The next product, the A320, was again a technological milestone. That was 16 years after the A300 release and indeed about 20 years after the start of the program - but by no means the first good product from Airbus.
Back to topic, Comac is not starting with a bang like Airbus did - but they don't have to. Same quality, slightly different, slightly cheaper could work after reaching governement-aided critical mass. Such government aid got Airbus started and notably did not cripple it.
Well there are only 3 economic blocks that could possibly spend a trillion dollars and several decades on developing an aviation industry. I don't see anyone else capable who could step up.
But why are they not also getting into the 737-size market, if that's such a huge market? If even the questionable 737 MAX is sold out for decades, that sounds like a pretty lucrative market to be in. It sounds to me like if you build something that works, you will sell as many as you can build.
One chilling effect was what Boeing and the US gov't did when Bombardier in Canada developed their own 100-130 seat brand new ("clean sheet") aircraft. They levied so many tariffs that the project was economically unviable.
So Bombardier sold it all to Airbus. Now Airbus has two series of single-aisle aircraft that are more competitive than Boeing's 737 (the A220 and A320.)
One can imagine how bad things must be behind the scenes if with that level of protectionism and political security deals backing the planes are grounded constantly. In working capitalism it's not the csuits that decide to make a great product, it's the competitive situation that forces everyones hand. Imagine Boeing as a ussr state owned conglomerate, who's directors try to game the metrics of the boss for a promotion. And we all know how that journey ended.
For the same reason Boeing developed the 737 MAX instead of a completely new model. The fixed costs are too high, the risks are too high, and the profit margins are too low. If it takes 10-15 years to develop a new plane, several years to ramp up production, and several years beyond that to break even, it does not make sense as a business. If you think it purely as an investment, there are always better uses for your money.
Wasn't a significant part of Boeing's decision to "recycle" the 737 time-to-market? Sure, they saved a bunch of money not designing a new plane, but they were also under heavy threat from the A320neo and needed to get something out there relatively quickly.
These are not in any way competitors to A320 and B737.
They are much smaller, with 2-2 seating, compared to 3-3 in the bigger jets. There are some routes and airlines where these are competitive; but they are not similar planes.
Mea culpa. Mostly. I relied on Wikipedia's characterization of the E2 series as similar to the Bombardier CSeries which was the subject of the American tariffs you reference. But the CSeries in fact became the A220, significantly smaller than the A320, so neither would it have been in the same category as the 737.
Both the E2 195 and the CSeries are well above the threshold of 100 passengers that Wikipedia uses as the maximum for a "regional jet", with the former holding up to 146 passengers and the latter up to 160. However, this is well behind the 737 MAX at 220 passengers. This classification apparently varies by source; 49 USC 41714 considers the maximum to be 71 passengers, while some sources take a threshold as high as 150 seats.
In any case, Embraer has gradually ramped up the maximum seating capacity on its planes, though you correctly point out that it has yet to take the middle-seat plunge.
So is Boeing! Companies without this massive amount of government support either barely survive on a tiny niche or fall over before actually shipping products.
It's fine that governments have decided to prop up these industries in their own ways, of course. Just hard to expect "free market" participants to show up and take on such a capital intensive industry
Up until recently there was also Bombardier, but it seems like they basically bankrupted themselves and ceded all of their commercial plane production to Airbus. Now they just do business jets.
China, a country with the biggest industrial GDP (ie not services or agriculture), spent 15 years on R&D to deliver so far only 4 airframes of an airliner that is technically behind comparable Boeing and Airbus airliners.
So not really a contradiction unless you are reading it too literally.
There's an apparent contradiction here.
China spent ~15 years developing the C919, and it's finally entering mass production. But it also appears to be sold out until the 2030s.
And here.