I case you're wondering, this "hydration" thing basically is a scam too, just like keto. Fun fact: it's generally impossible to die of dehydration, unless you genuinely don't have access to freshwater. People will drink when they're thirsty. No athletes have ever died of it. However, a significant number of athletes have died of over-hydration (water poisoning). Just like keto, it's dangerous and unhealthy.
Your level of unqualified certainty about keto diets is amusing. I personally know a number of people who are sticking to that diet and they've all had their health objectively improve as a result. (Weight, body tone, lipoprotein subfractions.)
In one case, he had chronic fatigue that his GP (family doctor) couldn't resolve, nor two expert referrals who tried medications and special diets. The keto diet led to an effective cure (the key factor was narrowed to the consumption of sugar, even relatively small amounts) and when combined with other health marker improvements, now considers his keto diet as necessary for a tolerable existence.
So yeah, dangerous and unhealthy.
(And for the record I've no idea what "this hydration thing" is. When I cited hydration I wasn't talking about some special diet, only to the basic concept of not being dehydrated.)
To ericb's point—there's a massive difference between a profit motive of selling optional advice versus selling the "product". Like many real diets, keto is little more than a subset of foods already available at the supermarket. It's not like someone was trying to flog a special powder or vitamin pills.