From description of the Great Old One pact:

The Great Old One might be unaware of your existence or entirely indifferent to you, but the secrets you have learned allow you to draw your magic from it

Patrons can have whatever motivation or lack of motivation the DM wants. I personally like there being some kind of RPing effect. Maybe some task you have to complete, punishment for acting against your patron, slowly eroding sanity. But none of that is necessary.