Why can't turbojets or turbofans be overtemped or overtorqued the way turboprops can?
You certainly can. The equivalent to overtorquing is called overboosting and is defined as an exceedance of the primary thrust setting parameter, N1 or EPR.

Modern FADEC engines contain software protection, but it is certainly possible in mechanically controlled engines. Thus, older aircraft, such as the DC-9 have mechanical or electronic controls which set N1/EPR bugs depending on flight condition and outside temperature.

EGT exceedances are also possible. Many, if not most, modern FADEC turbofans do not have EGT protection in normal operation so pilots do need to keep an eye on the EGT gauges during high power situations, especially when ambient temperatures are high and the engines are worn.