Asking internally the main reason seems to be around performance. When running targeted tests, it is faster to not have to do a compilation per test. (Tests can change environmental settings.) The tests take a while to run. Running them in production mode is more than just setting the environment variable - we need to fix up the tests to identify which ones adjust environment and would need redoing "production compilation". Certainly doable, just not done yet.
Having all these tests is of course great. However we are also thinking about how to make the tests modular. E.g. can you have the tests still work by adding a module? What if a new required table column is added? What if new fields are added on the screen? etc. So there are a few different things we would like to think through here. Not number one priority right now, but we definitely think about it.
Not sure if this is a possible community project - but it could be a bit boring (analyse the current tests to see how many change the environment etc). I can certainly provide examples of requirements I would like to see achieved! ;-)
And then there is the exciting effort to refactor the existing tests!
