They actually store multiple copies. They even use IPFS to store it over decentralized network.
But copyright is the main issue we don't see many services like open library or internet archive.
Rest in peace Aaron Swartz
tbf OP did mentioned it varies from genetics to genetics. 7-7.5 hrs is actually good spot. Mostly 8 hrs is recommended. For me 6 hrs is enough, but it also depends upon the work you are doing in your day to day life.