Getting maths correct is actually a hard problem to solve. Reading the problems that engineers have had over the years with floating point numbers will give you an insight into the situation.

http://floating-point-gui.de/xkcd/

A good quality math library that is optimised to take advantage of new processor extensions whilst still being correct is worth a lot.

I would imagine that there is a lack of engineering time to make this open source, rather than some nefarious purpose.