Why do certain people get epilepsy?

Varies. Causes of epilepsy include gestational or birth injuries, or even genetic brain malformations, later on head trauma, strokes, hypoxia, toxins, medication reactions, brain infections, brain tumors, ateriovenous malformations, hemangioblastomas, leukodystrophies, multiple sclerosis, neurofibromatosis, etc. In essence, any process causing damage or scarring to brain tissue.