So a human digestive system is generally acidic, especially at the stomach part, when it goes down to even 1.5 pH. Similar things must be happening in other mammals and to an extent, probably in all animals. Is there however some hard evolutionary, biological, chemical or any other block stopping the digestive system from being alkali and having stomach juices to be instead be pH 13 and still do their job?
Of course it doesn't have to be that extreme, my question comes down to having a generally alkaline system.
Also, it's set in a context of an alien biosphere, so the only limitation really is the fact of the life being eukaryotic and carbon-based, everything else is on the table