Because they replaced barbiturates with benzodiazepines. Benzodiazepines are much safer, and it is practically impossible to commit suicide. With barbiturates, a few tablets with a glass of whiskey were enough.
In clinical practice, barbiturates appear to be more dangerous than benzodiazepines, and this can be traced back to their respective mechanisms of action. Benzodiazepines increase the opening frequency of GABAA channel receptors in a GABA-dependent manner, while barbiturates increase the opening time and permeability to Cl- ions by interacting directly on the channel even in the absence of GABA. For this class of drugs, therefore, the control effect operated by natural neuronal activity is lost, and this is why barbiturates can induce serious effects such as coma at doses relatively close to therapeutic ones, while the doses of benzodiazepines necessary to have neurodepressant effects serious are very far from therapeutic doses.