The genome can be associated with a library, in that both store large volumes of information. So a population bottleneck is like a library fire in which a large percentage of the books are destroyed. If a fire destroys 90% of the books, only 10% remain to be copied, read and understood for future generations.
A well known example is the destruction of the Library of Alexandria. It is speculated that a huge amount of cultural knowledge was lost in its destruction.