Computation of reals: floating point vs TTE vs domain theory vs etc
I work in real-number computation, and I wish I knew the real answer. But I can speculate. It's a sociological problem, I think.

The community of people who work on exact real arithmetic consists of theoreticians who are not used to developing software. So they usually relegate the task of implementation to students (a notable exception is Norbert Müller's iRRAM), or they have their own toy implementations.

People who do have the necessary programming mojo do not have the necessary theoretical background. Without solid theoretical footing it is difficult to design exact real arithmetic correctly. For instance, it is a mistake to add lots of real numbers in a for loop, as you will get unacceptable performace due to loss of precision. If you want to add lots and lots of reals, you should do it with a tree-like structure, taking into account the magnitudes of the partial sums. Another thing which is difficult to get across is that &lt; and = as total boolean function on the reals simply do not exist (you can have = but it either returns false or it diverges, and &lt; diverges when given two equal reals).

Lastly, it is not clear at all that we know how to implement libraries for exact real arithmetic. They're not the usual pieces of libraries which just define some datatypes and some functions on them. Often exact real arithmetic requires special modes of control. For instance, iRRAM takes over the main execution of the program (it literally hijacks main), as well as standard input and output, so that it can rerun the program when loss of precision occurs. My library for real arithmetic in Haskell happens in a Staged monad (which is essentially the Reader monad). Most people expect the real numbers to be "just another datatype", but I have my doubts about that.