Kindle App Restrictions?

I was enjoying a nice sunny afternoon reading in the Kindle App on my iPhone, everything was great until I finished the book and wanted to get another one. WHY DOES APPLE CONTINUE TO BLOCK KINDLE USERS FROM USING THE WHOLE APP?!! I could only see KindleUnlimited and Kindle Vella books. Do I still have to go behind and through my legs to switch something from one hand to the other hand just to purchase a new book?!