why resonance is not considered in RC and RL Circuit
For resonance to occur, energy needs to flow from one component to another and back.

Resistors (R) can only absorb electrical energy and convert that into heat. Then the electrical energy is "lost" and it cannot be retrieved through the resistor.

Capacitors (C) and Inductors (L) however can store and release electrical energy.

So with an RC and RL circuit the energy "escapes" (as heat) through the resistor.

In an LC or RLC circuit, the energy goes back and forth between the Capacitor and Inductor making resonance possible.