Also because when you have operations with very differing range you they end up computed at the worst precision level without regard to the effects. In a fixed point implementation you would make the two scales different types and when doing computation involving both get an opportunity to preserve the precision. E.g. by dividing down the larger range one first rather than letting the smaller range one get crushed by the worst precision

Often these issues can be handled with very careful floating point order of operations (so long as -ffast-math isn't used...) but since its all implicit it's very easy to get wrong, while in fixed point you're forced to confront the scalings of different variables explicitly.