The role of a board as a group is to provide governance for the company and accountability to the management team. The typical board member is a venture capitalist that had to win the deal in a competitive round, or was appointed by a founder. That’s a bad starting relationship for effectively executing those jobs.
Plus, it’s a hard thing to do. People without operating backgrounds (at least 50% of board members I’ve seen) would have no experience doing these things at any scale.