y is china unable to build large aircraft?

hi everyone, i’m new here and also an amateur… anyways, there’s a question i always wondered abt….

its general believed that china’s military technology is a generation (roughly 20 yrs) behind the US… however, so far china has not been able to produce large aircraft… whether large transports such as a C-5, C-130, Il-76, or An-124… bombers like the b-52, b-1a/b, tu-22, tu-95, or tu-160… or civilian airliners such as 737, 747, A300, or tu-154…. these planes i mentioned r all over 20 yrs old… some much more than that… y is china unable to produce sth that both the US n russia / former soviet union could produce w/ technology from many decades ago?

i’d appreciate it if some1 can provide me w/ an answer