This is because the ending of Avengers: Infinity War, and Thanos’ Infinity Stone-based genocide, bled into the final moments of Ant-Man and The Wasp’s post-credits scene, leaving Scott stuck in the Quantum Realm, while the entire Pym family was dusted.
Nobody from the Ant-Man corner of the MCU appeared in Infinity War, but they will have big roles to play moving forward as everything comes to a head.
Of course, while this tweet shows Scott Lang and Hope van Dyne standing proudly (at least, the lower halves of their bodies are standing proudly), audiences who have seen Ant-Man and The Wasp already know that some serious work will need to be done to bring them back together.