Why is absorption across the lining of the stomach difficult for most chemicals and nutrients?

Absorption across the lining of the stomach is challenging for most chemicals and nutrients due to the stomach's thick mucosal barrier and the acidic environment, which can denature proteins and hinder the stability of many compounds. Additionally, the stomach's primary function is to digest food rather than absorb nutrients, leading to a relatively short contact time for substances with the stomach lining. Most nutrient absorption occurs later in the digestive tract, particularly in the small intestine, where conditions are more favorable for absorption.