Here's why:
* It refers to a general concept: "Skills" represents the overall ability to do something, not individual, separate items.
* You can't count skills individually: You wouldn't say "I have two skills" - you'd say "I have many skills" or "I have good skills."
* We use singular verbs: "My skills are improving."
However, there are a few exceptions:
* Specific types of skills: You can count specific types of skills, like "programming skills" or "communication skills."
* When referring to specific, learned abilities: You might say "He learned three new skills in the course."
In general, it's safer to treat "skills" as uncountable unless you're talking about specific types of skills or learned abilities.