It's tempting to treat a spelling mistake as a minor, cosmetic issue, especially on a busy catalog with hundreds of listings. In most places on a website, that's a fair way to think about it. A product description isn't most places, it's specifically the text a store is relying on to convince a stranger to hand over their card details.
It undermines the one thing the page is trying to do
A product description exists to build enough confidence for someone to buy. A visible typo works directly against that job, it's a small, concrete signal that nobody proofread this before publishing it, and if nobody checked the spelling, a cautious shopper starts wondering what else wasn't checked, like whether the size chart is accurate or the return policy is actually honored.
It's disproportionately visible
A typo buried in a long blog post can slide by unnoticed. A typo in a three sentence product description sits right next to the buy button, in text the shopper is actively reading with intent to purchase. There's nowhere for it to hide, and it gets read carefully by exactly the audience most likely to notice.
Why it keeps happening anyway
Most stores don't have someone whose job is proofreading every listing, especially smaller ones adding new products regularly. Descriptions get written quickly, sometimes by whoever's available that day, and get published without a second read. It's not negligence, it's just that manually proofreading an entire catalog doesn't scale well as a one person or two person task.
That's the specific gap an automated pass is good at closing, catching the kind of genuine typo a busy person would miss, without flagging brand names or technical terms as errors just because they're unfamiliar words.