It used to be poor political interference and two schizophrenic major customers (BOAC and BEA), that crippled the industry, now it's crap management at BAE and short term thinking.
The RJX was thought of in the early 1990's as a twin, with two newer engines as part of a general upgrading, if approved it could have hit the market in 1997/8, bet it would have sold well.
Instead, poodle along with the RJ
, then go for a minimum change new version, and they lost the lot, not that BAE had any love for the RJ
Same people who screwed up the Nimrod MRA.4 (those who knew warned that each wing/fuselage join was slightly different, BAE ignored them then found that the new wings don't fit), the new Concorde Lav design (heavier not lighter, no provision for cooling, poor waste management system) and much else besides.
To think how great BAC was, BAe for the first decade too.