There are resources on the moon. Like helium which the sources on Earth are slowly depleting because helium that gets released in to the air is basically gone, it floats up to the upper layers of the atmosphere and some atoms will eventually get knocked into space and leave Earth’s gravity. Also some scientific experiments require low gravity. Currently they are doing them on the ISS or in a reduced-gravity aircraft. In a moon base you can do a lot more science with more people.

Also some people that are researching lab grown organs think that in order to grow an entire organ that it has to be done in low gravity. So imagine in the future we could have a moon base that grows organs for thousands of people at a time.