Generally for stainless you go one step down in size the tool can do, but also the 1442 CAN do 3/8" which isn't included in the set, people do it. So can still do 5/16" / M8, it's just a fair bit more effort.
There is demand for the all metal type caps, and i suppose people like them. Though I'm unsure fully why or if people think the metal parts are doing the sealing. The seal mainly comes down to the gaskets & o-rings mainly, and the quality of thread engagement regardless of what its made from -...
They do offer that now as well
https://tite-reach.com/collections/tite-reach-wrenches/products/3-8-professional-tite-reach-extension-wrench-low-profile-socket-set-combo
Oh the engineers know, 100%. They could tell you all about it.
The larger the corporation is, and we make tools for many of them, the further away engineers sit (literally and figuratively) from those who work on packaging, marketing material and frankly even decision making. Locked in a box and...
TS29 is still in production, just back ordered. TS21 is on hiatus, raw material prices have spiked in cutting tools on the manufacturing end so we can only produce in large volumes to make things feasible. Items with lower demand in these categories we'll have to see if things stabilize.
For...