Car Oil Leak can be caused by a Bad Oil Seal. Oil Seals stop oil from leaking out when an engine or car part moves. When Oil Seals go bad oil is able to escape. Oil Seals can fail due to age, dirt, dust and lack of use. Cars older than 10 years are likely to have bad Oil Seals. Cars that sit around for long periods of time can have an Oil Leak as Oil needs to move to protect the Oil Seal from going bad.
If pressure builds up in an engine in places where it was not meant to it can push oil out. Worn out engines that allow engine gases to escape and bad PCV Valves can cause this.
Bolts not tightened down correctly so not enough pressure on the gaskets to form a good seal.
Car Oil Leak can be caused by a bad repair. Maybe a seal was not replaced, gasket not cleaned off fully before new gasket added. Maybe the wrong oil was put in which attacked the seal making it no longer work.
Hose taken off that was needed. Oil pressure sensor removed.
Heat can thin out the oil making it too thin for the seals.
Cold makes oil like sludge which can increase pressure as it does not flow.
Only so much oil is supposed to be put in the engine. If too much is put in then it can start to reach places that are not protected from leakage.