That's fine if you have a few 10s of billions to risk building products that might never be bought. There are 2 key issues here: you have to convince people th

That's fine if you have a few 10s of billions to risk building products that might never be bought. There are 2 key issues here: you have to convince people these will work for a decade plus without issue despite being new AND you have to convince a large number of people (companies, municipalities etc) (>100 to make the factory viable and get the economies of scale) who actually have the cash to buy them. This is a key moat for a lot of tech: anyone could design a decent airliner. Can you convince enough airlines to order them to make it viable to mass manufacturer them, despite having no name or track record? Hence Boeing and Airbus remain the only games in town (and Airbus only got there with a lot of state assistance).