"Not dead which eternal lie
stranger eons Death may die"
Actually, "That is not dead which can eternal lie, and with strange aeons even death may die" or
La mayyitan ma qadirun yatabaqqa sarmadi
Fa idha yaji' al-shudhdhadh fa-l-maut qad yantahi.
As the mad author of the Necronomicon puts it.
Anyways, Cthulhu cultists are people just like you - only we occasionally sacrifice a virgin or two to our blasphemous, alien God.
'In His House at R'lyeh Dead Cthulhu waits dreaming,
yet He shall rise and His kingdom shall cover the Earth.'
Or to quote from "Call of Cthulhu":
Then, whispered Castro, those first men formed the cult around small idols which the Great Ones shewed them; idols brought in dim aeras from dark stars. That cult would never die till the stars came right again, and the secret priests would take Great Cthulhu from His tomb to revive His subjects and resume His rule of earth. The time would be easy to know, for then mankind would become as the Great Old Ones; free and wild and beyond good and evil, with laws and morals thrown aside and all men shouting and killing and revelling in joy. Then the liberated Old Ones would teach them new ways to shout and kill and revel and enjoy themselves, and all the world would flame with a holocaust of ecstasy and freedom."
That a good enough explanation?