Organizing a team takes a long time, it takes many seasons. What happened at Manchester United is that each new coach who appeared immediately made many new signings without first going through a season to properly analyze the squad, the league and the opponents. As a consequence of this error, they spent a lot of money on new signings and the team didn't even win the Premier League.

Manchester United have had 11 managers in the last 10 years: https://www.transfermarkt.com/manchester-united/mitarbeiterhistorie/verein/985

Liverpool have had 2 coaches in the last 10 years: https://www.transfermarkt.com/fc-liverpool/mitarbeiterhistorie/verein/31

Manchester City have had 3 coaches in the last 10 years: https://www.transfermarkt.com/manchester-city/mitarbeiterhistorie/verein/281

Arsenal have had 3 coaches in the last 10 years: https://www.transfermarkt.com/arsenal-fc/mitarbeiterhistorie/verein/11

Manchester United need a good coach for the long term