Lots of words or phrases in English are used incorrectly so often that they start to look wrong when used in the correct way.
One of the commonest such errors is using ‘comprise of’, instead of ‘comprise’.
Collins Dictionary defines ‘comprise’ as ‘to include, contain’. So if you say ‘The board comprised of five members’ you are saying ‘The board included of five members’ or ‘The board contained of five members’.
The problem is that people see the wrong construction so often that they assume it’s right, and hardly anyone consults a dictionary to find out what a word’s exact meaning is. Everyone follows general usage like sheep, and the correct usage starts to fall by the wayside.