Why don't we switch to C like floating pointed arithmetic instead of automatic expansion to reals?

[Walter Bright via Digitalmars-d]

On 8/6/2016 2:48 AM, Ilya Yaroshenko wrote:
>> I don't know what the point of fusedMath is.
> It allows a compiler to replace two arithmetic operations with single composed
> one, see AVX2 (FMA3 for intel and FMA4 for AMD) instruction set.

I understand that, I just don't understand why that wouldn't be done anyway.