In Agents of S.H.I.E.L.D. season 5, every police department has the pictures of the agents that are the most wanted (including Coulson), why didn't Tony Stark (with eyes everywhere) know about Coulson's situation.
Because Coulson is Schrodinger's Cat, he's both alive and dead.
In Agent's of S.H.I.E.L.D. he's alive (even if Tony Stark happens to visit).
In the MCU movie universe, he's dead.
Why? Josh Whedon says so.
“It’s a weird little yes and no. As far as I’m concerned in the films, yes he’s dead. In terms of the narrative of these guys [The Avengers] his loss was very important. When I created the television show, it was sort of on the understanding that this can work and we can do it with integrity, but these Avengers movies are for people to see the Avengers movies and nothing else. And it would neither make sense nor be useful to say ‘Oh and by the way remember me? I died!’”