You're talking about literally some sort of steroid user, pro-bodybuilder cutting diet.  Those people don't seem to care about side effects like having zero energy and mostly only care about physical results.  For other people, constantly switching on and off keto every few days would be far more negatives than positives.  

Its also very difficult to alter your eating habits to get started, but once you do, it's not that hard to keep going.  But constantly going on and off would make most people cheat too much or even end up in some limbo of not utilizing ketones or glucose for fuel and probably having some medical issues from that from producing zero energy at all.  And why is it "negativity" calling digital shitcoins scams when they really are Keynesian scams based on artifical scarcity with built-in, rent seeking middlemen that don't remove counterparty risk?