Re: Ready for the down votes, but...
First of all, most catchers can be very good and very precise jammers. They use a virtually identical hardware and software - a small cell (aka femtocell). You just re-configure it to give a permanent reject. There is even a code which shuts down a phone so hard you need to do a hard reset on it (though in the past some manufacturers failed that test as it is not mandatory in the 3GPP spec).
The whole affair is the usual "We will not tell you the real reason".
The real reason is different - up to 3G the network authenticates the phone, but the phone DOES NOT authenticate the network. In 4G the phone will authenticate its home network - it is a 2 way auth if memory serves me right (if the operator has enabled it). As a result, the bog standard IMSI catchers stop working - you can evade them by limiting your phone to 4G only. The catcher now needs to be authorized by the operator and in some cases actively talk to the operator backend systems.