The Hargreeves found out that the apocalypse was planned for 2019. Another event in season 2 could have been the true moment The Umbrella Academy unraveled history and the timeline altogether: the destruction of The Commission.
The mere existence of the Sparrow Academy could be another sign that the Herb Commission is simply not up to scratch. In season 1 of The Umbrella Academy, the 2019 apocalypse was considered a fixed event in the eyes of The Commission.
Even considering the possibility that the apocalypse could have been triggered by something else, or that the Commission clearly changed its mind about bringing Armageddon to an unsuspecting 2019 at The Umbrella Academy.
The Herb Commission may lack the workmanship, allowing wrinkles to seep into the fabric of time. By defeating The Commission, The Umbrella Academy has killed the people who would have safeguarded their own creation.
Heading into season 3 of The Umbrella Academy, the Hargreeves brothers will undoubtedly fight to clarify the timeline. Maybe Herb shows up, realizes that the Commission has been wrong and both parties are working together to fix things.
Knowing that they were partly (mostly) responsible for the disaster would surely be motivation enough for the Academy to agree on The Umbrella Academy.