Well, we can only speculate. But I would suggest that since the writer themselves is choosing to write an op-ed on the subject, perhaps they themselves have ample motivation to come up with a persuasive word to argue their case? Their goal is to educate normal people on these chemicals and in the piece they explain that the terminology commonly used is so scientific as to be meaningless to the general public. Hence the need for a more direct "forever chemicals" instead of PFAS/per-and polyfluoroalkyl substances, PFOA/Perfluorooctanoic acid or C8/8 carbon chain structure.