I think it might be because of the association between bowling and bars or bar-like environments. Community gathering areas, especially ones that might attract a mature crowd, invite a little adult humor.
She thought she'd make a quick buck doing a stock photo shoot, and bam! innuendo.
I would never sell my photos, not because of the heartbreak if nobody would want to buy them, but because I wouldn't want to be neither the face of incontinence or erectile dysfunction, nor do I want to become the next Hide The Pain Harold or Distracted Boyfriend.