There are a lot of features available on the website that aren't available on the apps. As usual, it comes down to a matter of how much user demand there is for something and what their budget for development is. They don't release information on how popular each feature is but I would guess that things like the tablebase aren't used often by the average player here.
If you do need it, it is a simple matter to open the website with a browser app and use it.
When I try to use the analysis feature on my mobile app I can't see the endgame tablebase. Looking online I see that the feature is available. What is the problem?