It's a good question. Rodent studies do show benefits to exogenous ketones added to normal chow. The problem there is that we don't generally eat chow (aside from not being rodents). All sorts of things added to chow cause differences in how much animals eat, the pattern of their eating (whether they binge, or constantly snack. or go longer between meals etc., highly palatable foods can make it more likely the animals will eat during what should be their less active period, we know that's bad for the brain and health in general). We know that exogenous ketones, just like short chain fatty acids like acetate and butyrate that they're related to chemically, and which give similar benefits when added to chow, have a strong flavour, likely to affect feeding behaviour.