How can a galaxy spanning civilisation fail. If life can spread to other worlds, unless you get FTL, how could you end all life in a galaxy

As such it seems impossible for life to have reached interstellar travel anywhere in the Milky Way before at most a few million years ago, otherwise we would see it.

Which is weird because life surely can’t be that rare in the entirety of space time.

Of course the galaxy could be teaming with non interstellar life, but once you reach mankind’s level of sentience and technology it dormant seem a massive jump to interstellar, and once that happens there’s no way to put the genie back in the bottle.

Though there is likely life throughout the galaxy, it's probably difficult for one sentient spacefaring race to find another habitable planet they'd be comfortable on, i.e., one with a similar atmosphere and mass. If it's a long way from your planet to another you'd care to set foot on, you're left with lots of space stations. But who wants to live in that precarity?