Why do so many cheap sprayers leak or stop holding pressure?

It's a recurring theme across high-trust community threads: budget sprayers commonly lose their ability to hold air pressure within a season or two, and seals degrade with chemical exposure. Reviewers who want longevity tend to favor brands with replaceable seals (Viton/Santoprene) and internal no-leak pump designs, or pay up for a sealed battery pump where the liquid never touches the pump mechanism.