What is the point of sending us back over and over again with no knowledge of our previous existence? How can we learn from our previous mistakes if we can't remember them?
When you pass from this life YOU may or may not desire to experience more lives in the physical world. You are not sent back by anyone. The purpose of living a physical life is for the experiences and learning how our choices affect what they are. If you do decide to have more physical lives, it is more like having children and sharing in their experiences. Each new life is a unique new individual, that while a part of you is also a separate identity.
"Previous existence" assumes that time is linear and this is a sequential process. From the framework of the afterlife time is simultaneous. Multiple reincarnational live can begin, located in different times, simultaneously. Each life exists in a different environment, different society and has different experiences. There is communication between lives, though not usually for the waking consciousness. In dreams our consciousness does leave the physical sequential time focus and is capable of "visiting" lives in other times. One of the reasons we do not consciously remember the details of what is occurring in our other lives is the need to focus on our present one. What some may call mistakes are still learning experiences
Also, another popularly held belief is that you meet the same people over and over again each time and they are in your life in some way. I recall seeing someone on television once, I can't recall who it was, I believe it was on a talk show, said that if you are meeting the same people over and over again in each lifetime, you're not learning anything.
Although you may have the same people in different lives, the relationships change. For example, mothers, fathers, sons and daughters may exchange roles in different lives. These provide different perspectives and learning opportunities. In some lives you are male, in some you are female, some rich, some poor etc. Tasting the varieties of possibilities is all part of the game.
To be honest, while I think I do BELIEVE in reincarnation, only because there seems to be so much evidence to support it, I don't understand the point of it. If you supposedly already know everything you need to know when you're "over there", then what is the sense of being born and/or reborn and made to forget and be sent here to relearn stuff you already know?
We never will learn "everything we need to know". This would cause reality to stagnate. There is always constant growth, creativity and the learning of new things. The is an endless series of dimensional levels and we are very close to the beginning of understanding how this all works. If you are truly curious on this subject, I highly recommend reading some of the Seth books by Jane Roberts.