"Sirens" were these creatures from mythology whose singing supposedly caused sailors to crash their ships upon the rocks. " Thus "bubblegum sirens" is an allusion to the female pop singers of a decade ago who made such music and had such a limited appeal, yet were seductive (temptresses). That being said, the sentence you gave is saying that there is a reason why Lady Gaga is unlike these women (yet it still leaves open the possiblity that she is a type of bubblegum siren herself, albeit one unlike those of a decade ago).
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