Question: Why does the units standard environement not overload frem and piecewise

Recently there have been some questions about the unit packages. I would like to add another one that has been on my desk for a while.

The Simple environement overloads the command frem and piecewise. The "most powerful" (can we say so?) environement Standard does not

{with(Units:-Simple)[]} minus {with(Units:-Standard)[]}
                       {frem, piecewise}

For example calculating the remainder of a length in mm does not work in the Standard environment

restart;
with(Units:-Simple):
convert(frem(1.234*Unit(m),Unit(cm)),units,mm);
                      4.000000000 Unit(mm)

restart;
with(Units:-Standard):
convert(frem(1.234*Unit(m),Unit(cm)),units,mm)
Error, invalid input: frem received 1.234*Units:-Unit(m), which is not valid for its 1st argument, x

Why is that?