Is listening to recorded explanatory university lectures given by professors, and made available on a private website for students, considered unlawful and a theft from students who do not take these courses with the professors?

If the professors do not object to their lectures being recorded and published, then there is no harm in benefiting from them by uploading them to websites. However, if they explicitly or customarily prohibit this, then it is not permissible for students to upload them, nor for others to benefit from them without permission.