Bacteria can't proliferate quite so well if the tampon doesn't stay in for too long. However, given its super absorbency (and being reportedly very uncomfortable to remove), these tampons likely weren't changed very frequently.
Rely's own information leaflet suggested changing "at least once a day", i.e. leaving it in for up to 24 hours.
By September 1980, when the CDC released its report, almost 300 cases of TSS had been recorded, mostly linked to tampon use. On 22nd September 1980, Procter & Gamble recalled the product.
Three lawsuits were brought against Procter & Gamble for TSS deaths relating to Rely tampons.
@vagina_museum latest data suggest to change every 4 to 6 hours (8h may be too long in some cases). And you can get TSS from a menstrual cup if worn too long. Any internal protection can be dangerous on this issue, not just tampons.
(Scientific opinion from Anses in 2018-2019 https://www.anses.fr/en/content/assessment-safety-feminine-hygiene-products)