Explain why selectivity and signal-to-noise ratio is improved in "tandem mass spectrometry" (MS/MS, SRM or MRM) compared

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Explain why selectivity and signal-to-noise ratio is improved in "tandem mass spectrometry" (MS/MS, SRM or MRM) compared to traditional MS performed as SIM (Single Ion Monitoring).This I know: Tandem mass spectrometry (MS/MS) combines two mass analyzers in one instrument. The principle of MS/MS is that a sample is ionized and mass analyzed in the first mass analyzer. A particular m/z value of interest is selected from the mass spectrum and directed into a collision cell containing a neutral gas. The ion is excited by collision with the gas (collision-induced dissociation). This generates fragment ions which are separated and recorded by the second mass analyzer.Now why is selectivity and signal-to-noise ratio improved by the MS/MS instrument, compared to single ion monitoring (SIM)?