Atman (Self) is often defined as Sat-Chit-Aanand. Sat implies forever/permanent/existence, Chit implies self revealing consciousness and Aanand generally implies bliss. Definition of something means all conditions should be satisfied at all time.
Emotions come and go so how can an emotion like bliss always be permanent? For example, bliss cannot be experienced while watching horror movie or while watching a bad dream. Also, Atman is everywhere whether we speak of living beings or non-living objects. How can bliss be associated with a non-living entity like stone? How can bliss be associated with living entity not capable of experiencing bliss for example certain microbes/insects/animals etc. Also, Atman is the knower of everything including bliss, how can it itself be bliss?
If Aanand is considered as Anant which means limitless/infinite, this confusion would not be there and Atman indeed is limitless/whole/infinite. The word bliss when used in the context of Atman should be seen in this light. It is true that the more mind abides in Self, the happier it is. So, the words bliss & aanand can be used in their general sense also but they cannot be the direct representative of permanence when used this way.
Perhaps a Sanskrit scholar can look into the origin of the words Anant & Aanand.