Sure, the real reason the snap didn't happen is behind the scenes stuff about how Marvel Studios and Marvel TV grew apart. But as to season 5, yes they traveled to the future and then they traveled back. However, the traveling to the future and back happened many times and the events that happened after they traveled back weren't always the same (for example in an earlier timeline Quake destroyed earth and in a later timeline she didn't). Since they came back before Thanos' appearance in New York, that was before Strange looked at the possible futures while on Titan. This means that the differences in what happens with SHIELD (and the confederacy, Graviton, etc.) could've created vastly different timelines (one where Quake and Graviton break the earth, one where Thanos fails, etc.). It's not that hard to justify this if you want to.