In The Avengers, Pepper invites Agent Coulson in, despite the disruption to their date night. She asks him to join in. When Tony asks Coulson to come during official consultant hours (as he is a consultant and not a team member), it is Pepper who coxes Tony by handing him the file, knowing it is about Avengers business. Even when Tony is reluctant and says that they should continue their date night, Pepper tells Tony to focus on the work regarding the Avengers and decides that she’ll be leaving for DC. Later on, she helps redesign Stark Tower to Avengers tower with residential quarters for each Avenger.
In Avengers: Endgame, the situation has changed. Pepper does not come out to greet any of the Avengers, despite being in the house. Tony is left to serve and entertain the guests. Pepper even sends Morgan to “save her daddy” from the Avengers as the conversation grows long; but doesn’t show up herself.
Not to mention the fact that, even as Rescue, she only interacted with Tony, Rhodey, and Peter (and briefly spared a glance for Stephen Strange).
It really makes me wonder how much trust Pepper lost in the idea of Avengers as a team.