Every possible belief exists. The clergy of each tradition merely repeat what they were told in their theological training. Reincarnation is widely assumed and accepted on the ground that it "makes more sense" than a single life. It might make more sense if I believed that we were designed for a spiritual purpose rather than evolved as a biological process.
Wiccans, whom I both know and read of in SM Stirling's The Protector's War, accept reincarnation and add a sentimental Summerland between incarnations. I thought that Gardner made this up, along with other things, but apparently the idea has a longer history. But why should we accept this version rather than any other imaginative account of a hereafter?