Here's why:

* Ionization: While H₂S can donate a proton (H⁺) to form the hydrosulfide ion (HS⁻), it does so only to a limited extent in solution.

* Equilibrium: The ionization reaction of H₂S is an equilibrium reaction, favoring the undissociated H₂S molecule. This means that most of the H₂S molecules remain intact in solution.

* Acid Dissociation Constant (Ka): The Ka value for H₂S is very small (around 1 x 10⁻⁷), indicating that it is a weak acid. A smaller Ka value means that the acid ionizes less readily.

In contrast, strong acids like hydrochloric acid (HCl) ionize completely in solution, meaning they donate all their protons readily.