I appreciate your long career in the industry. Nevertheless, the fact remains that reality in 2017 is that 1980s/1990s style regional flying is literally non-existent. Someone else has listed all what remains of the regional airline industry in the UK and explained why all these operations only work because of some very special circumstances (PSOs, monopoly through qirport ownership etc.). I am not going to rehash all that, but I find your insinuation that apparently all investors and aviation professionals are dimwits as they refuse to engage in regional flying not terribly convincing.
If you insist that regional flying is still an attractive market segment, I would suggest that we list all those European regional airlines operating today on a purely commercial basis? I will start with...
Germany: None.
OLT - gone, EAE - gone, Intersky - gone, Eurowings Mk. I - gone, Contactair - gone, Delta Air - gone, Dauair - gone, Cityair - gone, Cirrus Air - gone. I could go on with that list for hours. In Germany, there is not a single regional airline left operating with less than 50 seats. Not a single one. There are exactly three domestic routes left that could be seen as a 1980s/1990s style regional air service: bmi regional operates MUC-RLG with an ER3 - which is widely seen as a slot warming operation on behalf of Lufthansa. Then there is MHG-TXL on RNA, which is more or less a corporate shuttle operated with a leased Dornier 328 with seats also being sold to the public. And then there is FMO-STR on AIS Airlines with a Jetstream 32 - AIS is a Dutch flying school where newly qualified pilots can built up hours with a load of unsuspecting passengers in the cabin....
If you move to Italy, France or Spain, the picture is pretty much the same.
Aren't all commercial airliners built to order?
No. That is not how Airbus or Boeing or Bombardier operate.
Built to order:
https://en.wikipedia.org/wiki/Build_to_order
Similarly there are plenty of aged 30 something seaters still in service, just look at Eastern and Loganair as two examples, when these types come to the end of their service lives further route networks will be lost, in addition to those already lost, unless someone starts manufacturing such types again and apparently a company in Turkey has decided to do just that.
This programme in Turkey was not started because they see a big market for the TRJ328/TRP328. It is to allow the Turkish Aerospace Industry to get some experience in manufacturing an advanced aircraft, based on a proven design. Therefore, the Turkish Ministry of Transport, Maritime Affairs & Communications is heavily involved and propping up the company. The main purpose is to give the Turkish aerospace industry the knowledge and experience needed to built a homegrown 70 seater aircraft, the TRJ628 (and in the longer run, apparently military aircraft). The TRJ328 is only the stepping stone for that, and a fair share of the sales is not expected to be for passenger operations, but for military applications and special mission aircraft. Besides that, the Turkish still have to walk all the talk that I have been hearing since 2011. They were promosing the first delivery for 2018 and the plane is still only on the drawing boards...
As for anything else - if there was demand and money to be earned, someone would built Saab 340NGs, DHC8-100NGs, EMB120NGs. Nobody does, and it must be for a reason. There is so little money to be earned in regional flying nowadays that the few airlines that still can be bothered to do it simply cannot afford factory fresh aircraft. And those operators that can - subsidiaries or affiliates of legacy carriers -are no longer interested in that market segment as they have moved to 70-100 seater jets. So there is nobody who would be able and willing to fork out lots of money for newly-built 30 seaters and could pass them on at affordable 2nd hand prices after a couple of years. A good example is Austrian regional Intersky. They operated with some fairly knackered Q300s for many years and were barely able to survive. Then a new investor had the idea to add two factory-fresh ATR72-600 - Intersky was gone within a year as they were simply unable to earn the money to pay for such expensive equipment.
PS: Actually, there is one 40-50 seater still in production, the ATR42-600. Just check out the sales of that ATR-variant. In 2016, they sold 11 examples to 2 airlines - 8 to Japan Airlines and 3 to Bahamasair.