Why is Embedded Strictly C/C++
First of all: forget about "embedded" as that is not a useful distinction. The all-important property is "resource-constrained". The most important resource is often time, in which case we talk about real-time systems, but it can also be memory or power.


New language adoption is hard and rare. It requires re-training, new tools, and finding a good way to work with the new language. This is costly, especially for the early adopters. It is also a chicken-and-egg problem: without a large user base there won't be good quality tools and libararies, but without those there won't be a large user base. Hence a new language must have a big advantage over the existing ones, otherwise it won't stand a chance.
Most "recent" new developments in languages have been filling the gap between the available CPU power and what the user needs. In other words: they can be inefficient in speed, but compensate by being easier on the programmer. Think of the rise of languages like Java, Python, Perl, Tcl that are essentially run by an interpreter (maybe after some compilation) and make heavy use of dynamic memory management. But this does not match well with the resource-constrained world, where we want to get a) the most out of the available resources, even at the expense of more programming effort, and b) a predictable use of resources.
C and C++ (or a suitable subset) are still the highest level languages that are in common use (enough that good tools, sufficient trained programmers, and extensive libraries are all available) that can meet predictable space and time requirements that are not to far from what is possible on current hardware. The only contender is I think Ada, but it has suffered from a bad start: the first implementations were (perceived to be?) too slow and inefficient, and now (even though good implementations are available) the language has fallen a bit behind in features (compared to C++). Personally I think this is a pity, other things being equal I'd rather fly in a plane that is programmed in Ada than one that has been done in C or C++.