Not enough sales volume because when you want one they have never been available-Think how many hundreds of sales were LOST for that reason forcing folks to band aid up a stocker and race--so when they are available again ( ha ha) those guys won't toss what they built just to do another with that new block.
It has been a joke for over a decade now with zero signs of meaningful improvement in the near future.
Tooling exist--tooling does not need to be created again at high cost--That tooling need to be transported to China and hand delivered to a real company that has the CNC equipment and the desire to make a profit by producing a quality product with reasonable price.
China makes some crap and lots of it but--China also makes some darn good stuff--The new Sidewinder is produced by a modern company that IMO is second to NONE--IF you examine the alloy quality of the Sidewinder and the alloy quality of the guides and the perfect press fit of the seats and the perfection that is the CNC work you would see that it is World Class Quality
Now...the Chevy head they are making and the SBF head as well as new FE Ford head will soon dominate the market--they are all AWESOME units!!
The intelligent redesign of the water jackets in the Chevy head is astounding--those guys are smart!
It is like Japan after WW2--stuff from there was crap--now it is among the best stuff produced anywhere in the world--China is making that happen even faster--they will be on the moon soon and we will look up and think WTH!! Quality and markets EVOLVE--they are getting better FAST. They HAVE to to keep on keeping on
There already exists knock offs of Dart Chevy blocks--on Racejunk for cheap and ..Dart blocks are CHEAP over here already so there is room --it can be done men!

I just have to ad for the small block guys
I have been selling Mopar parts for over 25 years and over that time the one thing I know is that 90% of Mopar sales is big block so even as a Mopar guy I would not ever take a chance on anything small block Mopar--the market is so small it is unbelievable so you guys are screwed--I would bet my house you will not get another aftermarket block so better gather what is out there already--didn't say I don't love a small block--I do! But any parts dealer anywhere will tell you it is true.