Here's why:

* Gold is a noble metal: It is highly unreactive due to its stable electron configuration.

* Hydrochloric acid is a weak oxidizing agent: It's not strong enough to oxidize gold and break its chemical bonds.

To dissolve gold, you need a stronger oxidizing agent. This is achieved through a process called aqua regia, which is a highly corrosive mixture of concentrated nitric acid and hydrochloric acid, optimally in a molar ratio of 1:3.

In aqua regia:

* Nitric acid acts as the oxidizer: It oxidizes gold ions ($Au^{3+}$) from the gold metal.

* Hydrochloric acid reacts with the gold ions: It forms tetrachloroaurate(III) anions ($[AuCl_4]^−$), which are soluble in solution.

The reaction in aqua regia can be summarized as follows:

$Au + 3 HNO_3 + 4 HCl \longrightarrow [AuCl_4]^- + 3NO_2 + H_3O^+ + 2 H_2O$