I believe that there is a subtle semantic difference between skills and skill.
According to the Oxford English dictionary, the uncountable noun "skill" refers to the ability to do something well such as expertise while the countable noun "skill(s)" refers to a particular ability.
Moreover, Merriam Webster dictionary classifies "skill" into two categories. The first category refers to one's ability to use knowledge effectively and readily in execution or performance; and, the second category refers to a learned (or developed) aptitude or ability.
Is that why the plural form of "skill" is used for the learned or to-be learned ability of performing or executing a particular subject? For example, communication skills (instead of communication skill), English skills (instead of English skill), hairstyling skills (instead of hairstyling skill).
Some would say that the reason for using the plural form is that a subject requires a set of abilities for its performance or execution. If the semantic difference does not exist, this will be the sole reason for using the plural form. On the other hand, if the semantic difference exists, this will another reason .
I would appreciate your answer.