M&S have been doing that for ages; they approve reviews before publishing so these are the ones that made the cut; there are thousands! That's actually a really mild one compared to some which read like X-rated sissy porn. (Many have been removed but only because the product is no longer available.)
I can only assume a lot more men than women buy M&S knickers, so the high ratings are great publicity and it doesn't matter that logically knickers that suit/fit most men will not work well for most women. There are lines that do tops and bottoms modeled on traditional women's lingerie styles but designed for male bodies for exactly that reason. (Perhaps if people start writing reviews about how crap the penis coverage/comfort is, they'll delete those!) They used to have a "gender" flag so you could sort and filter a lot of these out (not all, some reviewers set it to F because they want the reviews seen by women who'd rather not see them) but that's gone, too.
Since COVID a LOT more people are ordering online so legit pants reviews are needed, and who has time to dig through the porn? Plus M&S underthings have gone seriously downhill (which may or may not have any link to these reviewers' frequently requesting construction changes to widen guessets, etc. to make the ladies' knickers more penis-friendly) and I'd say M&S are not good enough to be worth the trouble.
Here's a thread from Style & Beauty with some options for shopping elsewhere: https://www.mumsnet.com/talk/style_and_beauty/4762380-ms-knickers-reviews