What destroyed the Great Library at Alexandria?

This almost reads like an advocacy of government spending.  The answer is a little deeper than that.

One of the great tragedies of ancient history, memorialized in myths and Hollywood film, is the burning of the great library at Alexandria...What made the Museum and its daughter branch great were its scholars...Those scrolls and books were nothing without people to care for them, study them, and share what they learned far and wide. [emphasis added]

The author attributes the decline of the library from neglect from the government.  But it was the society at large that no longer valued it.  In the end, that is how it was lost.  Nobody cared.  How much does it cost to pay for a few scholars to take care of the place?  How much would it have cost to start copying the most important works and placing them in a secure place?  The Empire could have afforded that, even the rich members of that society could have afforded that, but nobody cared enough to do it.

Update:

This video will go into this post for some background to its significance, in case that needs to be explained.