Why there is no Individual Levels for Episode One? Half-Life 2 and Half-Life 2: Episode Two have it, so why not?

Since it's quite difficult to find a link to download this game on the Internet, I give you a link to a google drive. https://drive.google.com/file/d/1esjeeOr8vRJUWB7xHoa5qXL0TS0DvnXb/view?usp=sharing