Putting on my crazy cap
Yet speaking with utmost sincereity.
The reason we don't remember past lives is simple, we have never lived before! Our conciousness however, has been arround maybe for aeons and lived upon earth perhaps 1000s of times. What one learns during one's life is permanently imprinted in one's conciousness, though not in the physical brain, mind.
It's impossible for me to explain, as the conept of 'conciousness' is so profoundly deep that to try and make any logical sense of it would be utter folly!
You can for example view segments and experience moments from you past lives in your Akashic records in the astral (or rather the 'buffer zone' between the astral and the mental) plain.
The reason you are the way you are is greatly dictated by your past lives. Egos that dominate you today may have been built up in a past life and carried on by your conciousness, pride, shame, lust, sorrow, anger etc..
I for example am a very sexual person I must admit and have been so from a very young age, I attribute this to me probably having been a great lover in a past life!
(or just a regular perv)
(luckily?) I am somewhat repulsive to women in this life, lol, so I might attribute this as Karma getting back at me for my indulgence, and perhaps a chance for me to change my fornicating ways.
It may seem like I am living in an intricately deluded world inside my head, but I concur that so is every one else!