Do you agree: limit(ABS(x)^n,n,∞,1); => undef (One-sided limit: n≥0)

[parisse]

This is the difference between an interactive or non-interactive system. The CAS is non-interactive, it means that you can not ask "Is x>1?" during a computation (like in maxima) and the result must be usable in further computations. In this example, limit would return a piecewise function because the condition can be solved symbolically, but it's not always the case and it would be much more complicated to handle (sooner or later you are faced with combinatoric complexity explosion, especially if you don't have good algorithms to simplify piecewise functions).
Another point to remember is that Giac was primarily designed to do computations that are hard or impossible to do by hand, not these kinds of limits because in my opinion, they should not be solved with a computer, I mean the computer will not give any additional value to what a STEM student should know. Of course, they could happen in an intermediate computation, but then the user should have made appropriate assumptions on the parameter.