Assuming no nutritional defficiencies or anything of the sort, is there any reason to wait long between dry fasts?
IF you want to develop strong consistent base, 2 days fastin every seven, e.g. for a few months develops very strong base. That is waiting longer - 5 days. That means it will be easier to do in future and you develop a natural relation to fasting that is stable. That is a reason you might wait longer - to develop a strong underlying fasting strength.
If you are grinding every time then it is not sustainable long term. Also ‘people say’ to recover for 2x as many days as you fast afterwards. That is a reason.
To make it less mentally taxing? might be another.