Where does it say this? NICE guidelines state that they advocates a stepwise approach to managing common mental health disorders. It recommends offering, or referring people for, the least intrusive and most effective intervention first. Therefore, non-drug interventions (such as cognitive behavioural therapy [CBT]) should be the mainstay of treatment for many people with depression or GAD, with drugs generally reserved for more severe illness or when symptoms have failed to respond to non-drug interventions.
Also mild-moderate depression cannot be assessed by simply assessing suicide intention or risk, other factors such as self-harm, behavioural issues like alcohol, drugs, indulging in high risk behaviours, family history, onset of symptoms, other risk factors such as bereavement, trauma etc. None of this is ever properly assessed by a GP alone. Their job is to advise on medication options if appropriate and referral for assessment for CBT and/or talking therapy.