Why SCR cannot be used as a bidirectional switch?

Silicon Controlled Rectifiers (SCRs) cannot be used as bidirectional switches because they are designed to conduct current in only one direction. When forward-biased, an SCR can be triggered into conduction, but it cannot be turned off by simply reversing the voltage; it requires the current to drop below a certain threshold. This unidirectional characteristic limits their application in circuits where bidirectional current flow is needed, such as in AC applications. For such purposes, devices like TRIACs or bidirectional thyristors are more suitable.