Why do so many drug names end in 'HCL'?

A previous answerer almost got it right. Many drugs are practically insoluble in water, yet they are basic. Such drugs, being bases, can react with acids to form salts. These salts, if properly chosen, can be quite water soluble. Very commonly, salts formed by reacting bases with hydrogen chloride or hydrochloric acid (HCl) are quite water soluble. It is often important to have good water solubility in a drug to aid its dissolution in the stomach or to make it appropriate for percutaneous (injection, intravenous, etc.) use. These hydrochloride salts are designated by listing "HCl" after the drug name.

Many of the drugs are usually insolible. To make them soluble the substances are made salt with hydrogen and calcium ions which make the substance soluble in water. Note that HCl is also produced in the stomach and helps in digestion in the same way.

The active ingredient is sold as a salt with HCl, I believe.

so they will dissolve in the human body. it's hard for them to work if they don't