It’s because new religions always cherry pick the parts they like of old religions and then eventually replace them entirely. Judaism itself was just made up from parts of Zoroastrianism and Hellenism and Babylonian beliefs.
It’s all bullshit anyway so it hardly matters. Religions change as needed to meet the changing wants and needs of the people who follow them. A Christian from the time of the crusades would probably be horrified by what is considered to be Christianity today.