There are also the "minor" factors such as high(er) inlet
temperature near ground level, thermal cycling, noise and exhaust
gas temperature.

The last can be ameliorated by running a compound steam cycle
powered by the "waste" heat from the gas turbine combustion cycle.
This also improves total thermodynamic efficiency to be comparable
with IC engines; but with greater package volume.

That shouldn't matter so much with heavy haulage vehicles and the
duty cycle of them is better suited to has turbine deployment
anyway.

As for machining, "cheap" turbine blades can be made from a variety
of materials that are ostensibly difficult to machine; either by
lost-wax investment casting, or in the case of ceramics; growing the
material to the correct shape.

But one doesn't need materials frequently used in aircraft gas
turbines: At the end of WWII, due to lack of exotic alloys, Germany
was making cheap gas turbine blades from folded sheet alloy steel,
cooled internally by airflow bled from (IIRC) the first stage of the
compressor. Such blades had a rated life of about 100 hours; about
200 flights; but other parts of the engine usually failed before the
turbine blades. The technique of internal cooling has since been
re-invented at least twice.

Steel is by itself a good thermal insulator is no panacea. The
stress on the outer "skin" of a hollow blade will be under
compressive stress, trying to stretch its cooled core. Improving the
thermal conductivity (or just the wall thickness) reduces the
stresses and the skin temperature.

Various surface treatments can help to reduce the peak temperature
experienced by the steel of the structural blade. It should be
obvious that the surface treatments need to be applied with the
blade at about operating temperature to minimise the stress imposed
on the core and the surface coat. However, when the blade cools an
internal "tension" is likely to prevail, making for a situation
where a fracture could be "explosive". One mode of failure is for
the surface to flake-off, leaving the unprotected steel exposed to
the hot gases.

That doesn't matter in an aircraft because aircraft are subject to
close mechanical scrutiny, often mandated. Put them into a car that
might see a workshop every 2 years and run perhaps 1000 hours with
2000 full thermal cycles between cursory inspections and you have a
problem.

A gas turbine for normal automotive use has to be tougher than one
for aircraft. Even when maintenance is neglected, it has to have
similar reserves of safety, strength and durability to an IC engine.

'cause they are both hurting financially.  Also, this development has
been going on for fifty years without success so far, and they may have
concluded there IS no practical solution.

It used to be in the aerospace industry I'd read, every two or three
years, of such a breakthrough, either a new material or a new ceramic
coating method.  NONE of these really worked- well, a few worked but are
still so expensive they're only useful in military or expensive long
range commercial aircraft.