The "culture of winning" means nothing. Liverpool had that "culture of winning" in the 80s but its not a real thing. Once the squad and the manager change you are a different team and you have to start all over again.
Yes we have our problems and being content to keep getting top 4 is bullshit but United are in a situation where they are striving to finish in the top 4. Thats their goal and they failed to achieve it last season. This season they are currently 10th.
Their squad is an absolute mess and I don't see them winning the league for a long time either. Their best players are mostly ageing out too. You wont see the likes of Rooney, Falcoa or RVP win another title with them.