You reincarnate because when you die, you go to Heaven. In Heaven, some souls are made to feel like they have unfinished work to do on Earth or that they still have to learn crap. This feeling is constant and can be overwhelming, so you “voluntarily” go to a large group of souls and wait with them for a chance to be sent into another body, then live another lifetime in this loveless world never being relayed what work you have to do or what you’re supposed to learn.