Museums are there so we can preserve things and people can learn from them. The San Francisco earthquake was massive and the surviving hydrant is a piece of history that children and adults can look at, have their interest picqued, and decide to spend more time learning about that part of the city's history.
To anyone outside of the situation it would appear odd to commemorate a piece of metal as a remembrance of a tragedy, but to the people who lived every day in the neighborhood it might be different. If the community has positive memories of the hydrant and want to save it, there is no reason not to.
That is the fire hydrants home, that's where it belongs. How do you know it wants to sit in a museum and be admired by people? It survived an earthquake, probably because it wants to stay there. If the fire hydrant gave up, then the fire hydrant wouldn't be there. But no, the earthquake came and the fire hydrant is still there standing tall. That's the fire hydrants spot for life.
No, the fact that this fire hydrant survived an earthquake only means that it was decently engineered and built, as all of them should be anyway. Maybe giving the people responsible for building it should be more appropriate. A fire hydrant in a museum sounds silly to say the least.
California has three tectonic plates, and therefore has a few earthquakes a day. There are, on average, over one hundred earthquakes a day. There is nothing special about a fire hydrant that did not get destroyed during an earthquake. A fire hydrant cannot survive anything, anyways, since they are not alive.