What made you open the wall up to look? Looks like it was behind insulation, so of course a home inspector would miss that. They don’t move things to look, they only look at what is visible. They almost certainly have a clause in their own paperwork that protects them from missing something outside the scope of their inspection (ie something hidden behind a wall or behind insulation). What you have here is a cracked foundation that has been repaired, crudely, but repaired. Unless there was a significant water incident caused by this crack, there would be no need for a previous owner to report it in disclosure. If there was no event, then if you were to go after them, they can easily say that they found the crack and repaired it prior to any issues.